draft-ietf-httpapi-rfc7807bis-07.unpg.txt		draft-ietf-httpapi-rfc7807bis-latest.txt
	HTTPAPI Working Group M. Nottingham		httpapi Working Group M. Nottingham
	Internet-Draft		Internet-Draft
	Obsoletes: 7807 (if approved) E. Wilde		Obsoletes: 7807 (if approved) E. Wilde
	Intended status: Standards Track		Intended status: Standards Track
	Expires: October 25, 2023 S. Dalal		Expires: April 8, 2025 S. Dalal
	April 23, 2023		October 5, 2024
	Problem Details for HTTP APIs		Problem Details for HTTP APIs
	draft-ietf-httpapi-rfc7807bis-07		draft-ietf-httpapi-rfc7807bis-latest
	Abstract		Abstract
	This document defines a "problem detail" to carry machine-readable		This document defines a "problem detail" to carry machine-readable
	details of errors in HTTP response content to avoid the need to		details of errors in HTTP response content to avoid the need to
	define new error response formats for HTTP APIs.		define new error response formats for HTTP APIs.
	This document obsoletes RFC 7807.		This document obsoletes RFC 7807.
	Status of This Memo		Status of This Memo
	skipping to change at line 35 ¶		skipping to change at page 1, line 36 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on October 25, 2023.		This Internet-Draft will expire on April 8, 2025.
	Copyright Notice		Copyright Notice
	Copyright (c) 2023 IETF Trust and the persons identified as the		Copyright (c) 2024 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Notational Conventions		2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
	3. The Problem Details JSON Object		3. The Problem Details JSON Object . . . . . . . . . . . . . . . 4
	3.1. Members of a Problem Details Object		3.1. Members of a Problem Details Object . . . . . . . . . . . 6
	3.1.1. "type"		3.1.1. "type" . . . . . . . . . . . . . . . . . . . . . . . 6
	3.1.2. "status"		3.1.2. "status" . . . . . . . . . . . . . . . . . . . . . . 7
	3.1.3. "title"		3.1.3. "title" . . . . . . . . . . . . . . . . . . . . . . . 7
	3.1.4. "detail"		3.1.4. "detail" . . . . . . . . . . . . . . . . . . . . . . 7
	3.1.5. "instance"		3.1.5. "instance" . . . . . . . . . . . . . . . . . . . . . 8
	3.2. Extension Members		3.2. Extension Members . . . . . . . . . . . . . . . . . . . . 8
	4. Defining New Problem Types		4. Defining New Problem Types . . . . . . . . . . . . . . . . . 9
	4.1. Example		4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 10
	4.2. Registered Problem Types		4.2. Registered Problem Types . . . . . . . . . . . . . . . . 10
	4.2.1. about:blank		4.2.1. about:blank . . . . . . . . . . . . . . . . . . . . . 11
	5. Security Considerations		5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	6. IANA Considerations		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	7. References		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
	7.1. Normative References		7.1. Normative References . . . . . . . . . . . . . . . . . . 12
	7.2. Informative References		7.2. Informative References . . . . . . . . . . . . . . . . . 13
	7.3. URIs		7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	Appendix A. JSON Schema for HTTP Problems		Appendix A. JSON Schema for HTTP Problems . . . . . . . . . . . 14
	Appendix B. HTTP Problems and XML		Appendix B. HTTP Problems and XML . . . . . . . . . . . . . . . 15
	Appendix C. Using Problem Details with Other Formats		Appendix C. Using Problem Details with Other Formats . . . . . . 17
	Appendix D. Changes from RFC 7807		Appendix D. Changes from RFC 7807 . . . . . . . . . . . . . . . 18
	Acknowledgements		Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 18
	Authors' Addresses		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
	HTTP status codes (Section 15 of [HTTP]) cannot always convey enough		HTTP status codes (Section 15 of [HTTP]) cannot always convey enough
	information about errors to be helpful. While humans using Web		information about errors to be helpful. While humans using web
	browsers can often understand an HTML [HTML5] response content, non-		browsers can often understand an HTML [HTML5] response content, non-
	human consumers of HTTP APIs have difficulty doing so.		human consumers of HTTP APIs have difficulty doing so.
	To address that shortcoming, this specification defines simple JSON		To address that shortcoming, this specification defines simple JSON
	[JSON] and XML [XML] document formats to describe the specifics of		[JSON] and XML [XML] document formats to describe the specifics of a
	problem(s) encountered -- "problem details".		problem encountered -- "problem details".
	For example, consider a response indicating that the client's account		For example, consider a response indicating that the client's account
	doesn't have enough credit. The API's designer might decide to use		doesn't have enough credit. The API's designer might decide to use
	the 403 Forbidden status code to inform HTTP-generic software (such		the 403 Forbidden status code to inform generic HTTP software (such
	as client libraries, caches, and proxies) of the response's general		as client libraries, caches, and proxies) of the response's general
	semantics. API-specific problem details (such as why the server		semantics. API-specific problem details (such as why the server
	refused the request and the applicable account balance) can be		refused the request and the applicable account balance) can be
	carried in the response content, so that the client can act upon them		carried in the response content so that the client can act upon them
	appropriately (for example, triggering a transfer of more credit into		appropriately (for example, triggering a transfer of more credit into
	the account).		the account).
	This specification identifies the specific "problem type" (e.g., "out		This specification identifies the specific "problem type" (e.g., "out
	of credit") with a URI [URI]. HTTP APIs can use URIs under their		of credit") with a URI [URI]. HTTP APIs can use URIs under their
	control to identify problems specific to them, or can reuse existing		control to identify problems specific to them or can reuse existing
	ones to facilitate interoperability and leverage common semantics		ones to facilitate interoperability and leverage common semantics
	(see Section 4.2).		(see Section 4.2).
	Problem details can contain other information, such as a URI		Problem details can contain other information, such as a URI
	identifying the problem's specific occurrence (effectively giving an		identifying the problem's specific occurrence (effectively giving an
	identifier to the concept "The time Joe didn't have enough credit		identifier to the concept "The time Joe didn't have enough credit
	last Thursday"), which can be useful for support or forensic		last Thursday"), which can be useful for support or forensic
	purposes.		purposes.
	The data model for problem details is a JSON [JSON] object; when		The data model for problem details is a JSON [JSON] object; when
	skipping to change at line 138 ¶		skipping to change at page 3, line 45 ¶
	naturally fit the semantics of 4xx and 5xx responses. Note that		naturally fit the semantics of 4xx and 5xx responses. Note that
	problem details are (naturally) not the only way to convey the		problem details are (naturally) not the only way to convey the
	details of a problem in HTTP. If the response is still a		details of a problem in HTTP. If the response is still a
	representation of a resource, for example, it's often preferable to		representation of a resource, for example, it's often preferable to
	describe the relevant details in that application's format.		describe the relevant details in that application's format.
	Likewise, defined HTTP status codes cover many situations with no		Likewise, defined HTTP status codes cover many situations with no
	need to convey extra detail.		need to convey extra detail.
	This specification's aim is to define common error formats for		This specification's aim is to define common error formats for
	applications that need one so that they aren't required to define		applications that need one so that they aren't required to define
	their own, or worse, tempted to redefine the semantics of existing		their own or, worse, tempted to redefine the semantics of existing
	HTTP status codes. Even if an application chooses not to use it to		HTTP status codes. Even if an application chooses not to use it to
	convey errors, reviewing its design can help guide the design		convey errors, reviewing its design can help guide the design
	decisions faced when conveying errors in an existing format.		decisions faced when conveying errors in an existing format.
	See Appendix D for a list of changes from RFC 7807.		See Appendix D for a list of changes from [RFC7807].
	2. Notational Conventions		2. Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in		"OPTIONAL" in this document are to be interpreted as described in
	BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	3. The Problem Details JSON Object		3. The Problem Details JSON Object
	The canonical model for problem details is a JSON [JSON] object.		The canonical model for problem details is a JSON [JSON] object.
	skipping to change at line 227 ¶		skipping to change at page 5, line 40 ¶
	},		},
	{		{
	"detail": "must be 'green', 'red' or 'blue'",		"detail": "must be 'green', 'red' or 'blue'",
	"pointer": "#/profile/color"		"pointer": "#/profile/color"
	}		}
	]		]
	}		}
	The fictional problem type here defines the "errors" extension, an		The fictional problem type here defines the "errors" extension, an
	array that describes the details of each validation error. Each		array that describes the details of each validation error. Each
	member is an object containing "detail" to describe the issue, and		member is an object containing "detail" to describe the issue and
	"pointer" to locate the problem within the request's content using a		"pointer" to locate the problem within the request's content using a
	JSON Pointer [JSON-POINTER].		JSON Pointer [JSON-POINTER].
	When an API encounters multiple problems that do not share the same		When an API encounters multiple problems that do not share the same
	type, it is RECOMMENDED that the most relevant or urgent problem be		type, it is RECOMMENDED that the most relevant or urgent problem be
	represented in the response. While it is possible to create generic		represented in the response. While it is possible to create generic
	"batch" problem types that convey multiple, disparate types, they do		"batch" problem types that convey multiple, disparate types, they do
	not map well into HTTP semantics.		not map well into HTTP semantics.
	Note also that the API has responded with the application/		Note also that the API has responded with the "application/
	problem+json type, even though the client did not list it in Accept,		problem+json" type, even though the client did not list it in Accept,
	as is allowed by HTTP (see Section 12.5.1 of [HTTP]).		as is allowed by HTTP (see Section 12.5.1 of [HTTP]).
	3.1. Members of a Problem Details Object		3.1. Members of a Problem Details Object
	Problem detail objects can have the following members. If a member's		Problem detail objects can have the following members. If a member's
	value type does not match the specified type, the member MUST be		value type does not match the specified type, the member MUST be
	ignored -- i.e., processing will continue as if the member had not		ignored -- i.e., processing will continue as if the member had not
	been present.		been present.
	3.1.1. "type"		3.1.1. "type"
	skipping to change at line 275 ¶		skipping to change at page 6, line 39 ¶
	When "type" contains a relative URI, it is resolved relative to the		When "type" contains a relative URI, it is resolved relative to the
	document's base URI, as per [URI], Section 5. However, using		document's base URI, as per [URI], Section 5. However, using
	relative URIs can cause confusion, and they might not be handled		relative URIs can cause confusion, and they might not be handled
	correctly by all implementations.		correctly by all implementations.
	For example, if the two resources "https://api.example.org/foo/		For example, if the two resources "https://api.example.org/foo/
	bar/123" and "https://api.example.org/widget/456" both respond with a		bar/123" and "https://api.example.org/widget/456" both respond with a
	"type" equal to the relative URI reference "example-problem", when		"type" equal to the relative URI reference "example-problem", when
	resolved they will identify different resources		resolved they will identify different resources
	("https://api.example.org/foo/bar/example-problem" and		("https://api.example.org/foo/bar/example-problem" and
	"https://api.example.org/widget/example-problem" respectively). As a		"https://api.example.org/widget/example-problem", respectively). As
	result, it is RECOMMENDED that absolute URIs be used in "type" when		a result, it is RECOMMENDED that absolute URIs be used in "type" when
	possible, and that when relative URIs are used, they include the full		possible and that when relative URIs are used, they include the full
	path (e.g., "/types/123").		path (e.g., "/types/123").
	The type URI is allowed to be a non-resolvable URI. For example, the		The type URI is allowed to be a non-resolvable URI. For example, the
	tag URI scheme [TAG] can be used to uniquely identify problem types:		tag URI scheme [TAG] can be used to uniquely identify problem types:
	tag:example@example.org,2021-09-17:OutOfLuck		tag:example@example.org,2021-09-17:OutOfLuck
	However, resolvable type URIs are encouraged by this specification		However, resolvable type URIs are encouraged by this specification
	because it might become desirable to resolve the URI in the future.		because it might become desirable to resolve the URI in the future.
	For example, if an API designer used the URI above and later adopted		For example, if an API designer used the URI above and later adopted
	skipping to change at line 308 ¶		skipping to change at page 7, line 23 ¶
	The "status" member, if present, is only advisory; it conveys the		The "status" member, if present, is only advisory; it conveys the
	HTTP status code used for the convenience of the consumer.		HTTP status code used for the convenience of the consumer.
	Generators MUST use the same status code in the actual HTTP response,		Generators MUST use the same status code in the actual HTTP response,
	to assure that generic HTTP software that does not understand this		to assure that generic HTTP software that does not understand this
	format still behaves correctly. See Section 5 for further caveats		format still behaves correctly. See Section 5 for further caveats
	regarding its use.		regarding its use.
	Consumers can use the status member to determine what the original		Consumers can use the status member to determine what the original
	status code used by the generator was when it has been changed (e.g.,		status code used by the generator was when it has been changed (e.g.,
	by an intermediary or cache), and when a message's content is		by an intermediary or cache) and when a message's content is
	persisted without HTTP information. Generic HTTP software will still		persisted without HTTP information. Generic HTTP software will still
	use the HTTP status code.		use the HTTP status code.
	3.1.3. "title"		3.1.3. "title"
	The "title" member is a JSON string containing a short, human-		The "title" member is a JSON string containing a short, human-
	readable summary of the problem type.		readable summary of the problem type.
	It SHOULD NOT change from occurrence to occurrence of the problem,		It SHOULD NOT change from occurrence to occurrence of the problem,
	except for localization (e.g., using proactive content negotiation;		except for localization (e.g., using proactive content negotiation;
	see [HTTP], Section 12.1).		see [HTTP], Section 12.1).
	The "title" string is advisory, and is included only for users who		The "title" string is advisory and is included only for users who are
	are both unaware of and cannot discover the semantics of the type URI		unaware of and cannot discover the semantics of the type URI (e.g.,
	(e.g., during offline log analysis).		during offline log analysis).
	3.1.4. "detail"		3.1.4. "detail"
	The "detail" member is a JSON string containing a human-readable		The "detail" member is a JSON string containing a human-readable
	explanation specific to this occurrence of the problem.		explanation specific to this occurrence of the problem.
	The "detail" string, if present, ought to focus on helping the client		The "detail" string, if present, ought to focus on helping the client
	correct the problem, rather than giving debugging information.		correct the problem, rather than giving debugging information.
	Consumers SHOULD NOT parse the "detail" member for information;		Consumers SHOULD NOT parse the "detail" member for information;
	skipping to change at line 349 ¶		skipping to change at page 8, line 17 ¶
	The "instance" member is a JSON string containing a URI reference		The "instance" member is a JSON string containing a URI reference
	that identifies the specific occurrence of the problem.		that identifies the specific occurrence of the problem.
	When the "instance" URI is dereferenceable, the problem details		When the "instance" URI is dereferenceable, the problem details
	object can be fetched from it. It might also return information		object can be fetched from it. It might also return information
	about the problem occurrence in other formats through use of		about the problem occurrence in other formats through use of
	proactive content negotiation (see [HTTP], Section 12.5.1).		proactive content negotiation (see [HTTP], Section 12.5.1).
	When the "instance" URI is not dereferenceable, it serves as a unique		When the "instance" URI is not dereferenceable, it serves as a unique
	identifier for the problem occurrence that may be of significance to		identifier for the problem occurrence that may be of significance to
	the server, but is opaque to the client.		the server but is opaque to the client.
	When "instance" contains a relative URI, it is resolved relative to		When "instance" contains a relative URI, it is resolved relative to
	the document's base URI, as per [URI], Section 5. However, using		the document's base URI, as per [URI], Section 5. However, using
	relative URIs can cause confusion, and they might not be handled		relative URIs can cause confusion, and they might not be handled
	correctly by all implementations.		correctly by all implementations.
	For example, if the two resources "https://api.example.org/foo/		For example, if the two resources "https://api.example.org/foo/
	bar/123" and "https://api.example.org/widget/456" both respond with		bar/123" and "https://api.example.org/widget/456" both respond with
	an "instance" equal to the relative URI reference "example-instance",		an "instance" equal to the relative URI reference "example-instance",
	when resolved they will identify different resources		when resolved they will identify different resources
	("https://api.example.org/foo/bar/example-instance" and		("https://api.example.org/foo/bar/example-instance" and
	"https://api.example.org/widget/example-instance" respectively). As		"https://api.example.org/widget/example-instance", respectively). As
	a result, it is RECOMMENDED that absolute URIs be used in "instance"		a result, it is RECOMMENDED that absolute URIs be used in "instance"
	when possible, and that when relative URIs are used, they include the		when possible, and that when relative URIs are used, they include the
	full path (e.g., "/instances/123").		full path (e.g., "/instances/123").
	3.2. Extension Members		3.2. Extension Members
	Problem type definitions MAY extend the problem details object with		Problem type definitions MAY extend the problem details object with
	additional members that are specific to that problem type.		additional members that are specific to that problem type.
	For example, our "out of credit" problem above defines two such		For example, our out-of-credit problem above defines two such
	extensions -- "balance" and "accounts" to convey additional, problem-		extensions -- "balance" and "accounts" to convey additional, problem-
	specific information.		specific information.
	Similarly, the "validation error" example defines an "errors"		Similarly, the "validation error" example defines an "errors"
	extension that contains a list of individual error occurrences found,		extension that contains a list of individual error occurrences found,
	with details and a pointer to the location of each.		with details and a pointer to the location of each.
	Clients consuming problem details MUST ignore any such extensions		Clients consuming problem details MUST ignore any such extensions
	that they don't recognize; this allows problem types to evolve and		that they don't recognize; this allows problem types to evolve and
	include additional information in the future.		include additional information in the future.
	skipping to change at line 393 ¶		skipping to change at page 9, line 15 ¶
	When creating extensions, problem type authors should choose their		When creating extensions, problem type authors should choose their
	names carefully. To be used in the XML format (see Appendix B), they		names carefully. To be used in the XML format (see Appendix B), they
	will need to conform to the Name rule in Section 2.3 of [XML].		will need to conform to the Name rule in Section 2.3 of [XML].
	4. Defining New Problem Types		4. Defining New Problem Types
	When an HTTP API needs to define a response that indicates an error		When an HTTP API needs to define a response that indicates an error
	condition, it might be appropriate to do so by defining a new problem		condition, it might be appropriate to do so by defining a new problem
	type.		type.
	Before doing so, it's important to understand what they are good for,		Before doing so, it's important to understand what they are good for
	and what's better left to other mechanisms.		and what is better left to other mechanisms.
	Problem details are not a debugging tool for the underlying		Problem details are not a debugging tool for the underlying
	implementation; rather, they are a way to expose greater detail about		implementation; rather, they are a way to expose greater detail about
	the HTTP interface itself. Designers of new problem types need to		the HTTP interface itself. Designers of new problem types need to
	carefully take into account the Security Considerations (Section 5),		carefully take into account the Section 5, in particular, the risk of
	in particular, the risk of exposing attack vectors by exposing		exposing attack vectors by exposing implementation internals through
	implementation internals through error messages.		error messages.
	Likewise, truly generic problems -- i.e., conditions that might apply		Likewise, truly generic problems -- i.e., conditions that might apply
	to any resource on the Web -- are usually better expressed as plain		to any resource on the Web -- are usually better expressed as plain
	status codes. For example, a "write access disallowed" problem is		status codes. For example, a "write access disallowed" problem is
	probably unnecessary, since a 403 Forbidden status code in response		probably unnecessary, since a 403 Forbidden status code in response
	to a PUT request is self-explanatory.		to a PUT request is self-explanatory.
	Finally, an application might have a more appropriate way to carry an		Finally, an application might have a more appropriate way to carry an
	error in a format that it already defines. Problem details are		error in a format that it already defines. Problem details are
	intended to avoid the necessity of establishing new "fault" or		intended to avoid the necessity of establishing new "fault" or
	"error" document formats, not to replace existing domain-specific		"error" document formats, not to replace existing domain-specific
	formats.		formats.
	That said, it is possible to add support for problem details to		That said, it is possible to add support for problem details to
	existing HTTP APIs using HTTP content negotiation (e.g., using the		existing HTTP APIs using HTTP content negotiation (e.g., using the
	Accept request header to indicate a preference for this format; see		Accept request header to indicate a preference for this format; see
	[HTTP], Section 12.5.1).		[HTTP], Section 12.5.1).
	New problem type definitions MUST document:		New problem type definitions MUST document:
	1. a type URI (typically, with the "http" or "https" scheme),		1. a type URI (typically, with the "http" or "https" scheme)
	2. a title that appropriately describes it (think short), and		2. a title that appropriately describes it (think short)
	3. the HTTP status code for it to be used with.		3. the HTTP status code for it to be used with
	Problem type definitions MAY specify the use of the Retry-After		Problem type definitions MAY specify the use of the Retry-After
	response header ([HTTP], Section 10.2.3) in appropriate		response header ([HTTP], Section 10.2.3) in appropriate
	circumstances.		circumstances.
	A problem's type URI SHOULD resolve to HTML [HTML5] documentation		A problem type URI SHOULD resolve to HTML [HTML5] documentation that
	that explains how to resolve the problem.		explains how to resolve the problem.
	A problem type definition MAY specify additional members on the		A problem type definition MAY specify additional members on the
	problem details object. For example, an extension might use typed		problem details object. For example, an extension might use typed
	links [WEB-LINKING] to another resource that machines can use to		links [WEB-LINKING] to another resource that machines can use to
	resolve the problem.		resolve the problem.
	If such additional members are defined, their names SHOULD start with		If such additional members are defined, their names SHOULD start with
	a letter (ALPHA, as per [ABNF], Appendix B.1) and SHOULD comprise		a letter (ALPHA, as per [ABNF], Appendix B.1) and SHOULD comprise
	characters from ALPHA, DIGIT ([ABNF], Appendix B.1), and "_" (so that		characters from ALPHA, DIGIT ([ABNF], Appendix B.1), and "_" (so that
	it can be serialized in formats other than JSON), and they SHOULD be		it can be serialized in formats other than JSON), and they SHOULD be
	three characters or longer.		three characters or longer.
	4.1. Example		4.1. Example
	For example, if you are publishing an HTTP API to your online		For example, if you are publishing an HTTP API to your online
	shopping cart, you might need to indicate that the user is out of		shopping cart, you might need to indicate that the user is out of
	credit (our example from above), and therefore cannot make the		credit (our example from above) and therefore cannot make the
	purchase.		purchase.
	If you already have an application-specific format that can		If you already have an application-specific format that can
	accommodate this information, it's probably best to do that.		accommodate this information, it's probably best to do that.
	However, if you don't, you might use one of the problem details		However, if you don't, you might use one of the problem detail
	formats -- JSON if your API is JSON-based, or XML if it uses that		formats -- JSON if your API is JSON-based or XML if it uses that
	format.		format.
	To do so, you might look in the registry (Section 4.2) for an		To do so, you might look in the registry (Section 4.2) for an
	already-defined type URI that suits your purposes. If one is		already-defined type URI that suits your purposes. If one is
	available, you can reuse that URI.		available, you can reuse that URI.
	If one isn't available, you could mint and document a new type URI		If one isn't available, you could mint and document a new type URI
	(which ought to be under your control and stable over time), an		(which ought to be under your control and stable over time), an
	appropriate title and the HTTP status code that it will be used with,		appropriate title and the HTTP status code that it will be used with,
	along with what it means and how it should be handled.		along with what it means and how it should be handled.
	4.2. Registered Problem Types		4.2. Registered Problem Types
	This specification defines the HTTP Problem Type registry for common,		This specification defines the "HTTP Problem Types" registry for
	widely-used problem type URIs, to promote reuse.		common, widely used problem type URIs, to promote reuse.
	The policy for this registry is Specification Required, per		The policy for this registry is Specification Required, per
	[RFC8126], Section 4.6.		[RFC8126], Section 4.6.
	When evaluating requests, the Expert(s) should consider community		When evaluating requests, the designated expert(s) should consider
	feedback, how well-defined the problem type is, and this		community feedback, how well-defined the problem type is, and this
	specification's requirements. Vendor-specific, application-specific,		specification's requirements. Vendor-specific, application-specific,
	and deployment-specific values are not registerable. Specification		and deployment-specific values are unable to be registered.
	documents should be published in a stable, freely available manner
	(ideally located with a URL), but need not be standards.		Specification documents should be published in a stable, freely
			available manner (ideally located with a URL) but need not be
			standards.
	Registrations MAY use the prefix "https://iana.org/assignments/http-		Registrations MAY use the prefix "https://iana.org/assignments/http-
	problem-types#" for the type URI. Note that those URIs may not be		problem-types#" for the type URI. Note that those URIs may not be
	able to be resolved.		able to be resolved.
	Registration requests should use the following template:		The following template should be used for registration requests:
	o Type URI: [a URI for the problem type]		Type URI: [a URI for the problem type]
	o Title: [a short description of the problem type]		Title: [a short description of the problem type]
	o Recommended HTTP status code: [what status code is most		Recommended HTTP status code: [what status code is most appropriate
	appropriate to use with the type]		to use with the type]
	o Reference: [to a specification defining the type]		Reference: [to a specification defining the type]
	See the registry at https://iana.org/assignments/http-problem-types		See the registry at https://iana.org/assignments/http-problem-types
	[1] for details on where to send registration requests.		[1] for details on where to send registration requests.
	4.2.1. about:blank		4.2.1. about:blank
	This specification registers one Problem Type, "about:blank".		This specification registers one Problem Type, "about:blank", as
			follows.
	o Type URI: about:blank		Type URI: about:blank
	o Title: See HTTP Status Code		Title: See HTTP Status Code
	o Recommended HTTP status code: N/A		Recommended HTTP status code: N/A
	o Reference: RFC nnnn		Reference: RFC 9457
	The "about:blank" URI [ABOUT], when used as a problem type, indicates		The "about:blank" URI [ABOUT], when used as a problem type, indicates
	that the problem has no additional semantics beyond that of the HTTP		that the problem has no additional semantics beyond that of the HTTP
	status code.		status code.
	When "about:blank" is used, the title SHOULD be the same as the		When "about:blank" is used, the title SHOULD be the same as the
	recommended HTTP status phrase for that code (e.g., "Not Found" for		recommended HTTP status phrase for that code (e.g., "Not Found" for
	404, and so on), although it MAY be localized to suit client		404, and so on), although it MAY be localized to suit client
	preferences (expressed with the Accept-Language request header).		preferences (expressed with the Accept-Language request header).
	skipping to change at line 554 ¶		skipping to change at page 12, line 32 ¶
	status code itself, bringing the possibility of disagreement between		status code itself, bringing the possibility of disagreement between
	the two. Their relative precedence is not clear, since a		the two. Their relative precedence is not clear, since a
	disagreement might indicate that (for example) an intermediary has		disagreement might indicate that (for example) an intermediary has
	changed the HTTP status code in transit (e.g., by a proxy or cache).		changed the HTTP status code in transit (e.g., by a proxy or cache).
	Generic HTTP software (such as proxies, load balancers, firewalls,		Generic HTTP software (such as proxies, load balancers, firewalls,
	and virus scanners) are unlikely to know of or respect the status		and virus scanners) are unlikely to know of or respect the status
	code conveyed in this member.		code conveyed in this member.
	6. IANA Considerations		6. IANA Considerations
	Please update the "application/problem+json" and "application/		In the "application" registry under the "Media Types" registry, IANA
	problem+xml" registrations in the "Media Types" registry to refer to		has updated the "application/problem+json" and "application/
	this document.		problem+xml" registrations to refer to this document.
	Please create the "HTTP Problem Types" registry as specified in		IANA has created the "HTTP Problem Types" registry as specified in
	Section 4.2, and populate it with "about:blank" as per Section 4.2.1.		Section 4.2 and populated it with "about:blank" as per Section 4.2.1.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234,		Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC5234, January 2008,		DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc5234>.		<https://www.rfc-editor.org/info/rfc5234>.
	skipping to change at line 638 ¶		skipping to change at page 14, line 23 ¶
	Schema: A Media Type for Describing JSON Documents",		Schema: A Media Type for Describing JSON Documents",
	draft-bhutton-json-schema-01 (work in progress), June		draft-bhutton-json-schema-01 (work in progress), June
	2022.		2022.
	[RDFA] Adida, B., Ed., Herman, I., Ed., Birbeck, M., Ed., and S.		[RDFA] Adida, B., Ed., Herman, I., Ed., Birbeck, M., Ed., and S.
	McCarron, Ed., "RDFa Core 1.1 - Third Edition", W3C REC		McCarron, Ed., "RDFa Core 1.1 - Third Edition", W3C REC
	REC-rdfa-core-20150317, W3C REC-rdfa-core-20150317, March		REC-rdfa-core-20150317, W3C REC-rdfa-core-20150317, March
	2015,		2015,
	<https://www.w3.org/TR/2015/REC-rdfa-core-20150317/>.		<https://www.w3.org/TR/2015/REC-rdfa-core-20150317/>.
			[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
			APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
			<https://www.rfc-editor.org/info/rfc7807>.
	[TAG] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",		[TAG] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
	RFC 4151, DOI 10.17487/RFC4151, October 2005,		RFC 4151, DOI 10.17487/RFC4151, October 2005,
	<https://www.rfc-editor.org/info/rfc4151>.		<https://www.rfc-editor.org/info/rfc4151>.
	[WEB-LINKING]		[WEB-LINKING]
	Nottingham, M., "Web Linking", RFC 8288,		Nottingham, M., "Web Linking", RFC 8288,
	DOI 10.17487/RFC8288, October 2017,		DOI 10.17487/RFC8288, October 2017,
	<https://www.rfc-editor.org/info/rfc8288>.		<https://www.rfc-editor.org/info/rfc8288>.
	[XSLT] Thompson, H., Ed., Clark, J., Ed., and S. Pieters, Ed.,		[XSLT] Thompson, H., Ed., Clark, J., Ed., and S. Pieters, Ed.,
	skipping to change at line 660 ¶		skipping to change at page 14, line 49 ¶
	xml-stylesheet-20101028, October 2010,		xml-stylesheet-20101028, October 2010,
	<https://www.w3.org/TR/2010/REC-xml-stylesheet-20101028/>.		<https://www.w3.org/TR/2010/REC-xml-stylesheet-20101028/>.
	7.3. URIs		7.3. URIs
	[1] https://iana.org/assignments/http-problem-types		[1] https://iana.org/assignments/http-problem-types
	Appendix A. JSON Schema for HTTP Problems		Appendix A. JSON Schema for HTTP Problems
	This section presents a non-normative JSON Schema [JSON-SCHEMA] for		This section presents a non-normative JSON Schema [JSON-SCHEMA] for
	HTTP Problem Details. If there is any disagreement between it and		HTTP problem details. If there is any disagreement between it and
	the text of the specification, the latter prevails.		the text of the specification, the latter prevails.
	# NOTE: '\' line wrapping per RFC 8792		# NOTE: '\' line wrapping per RFC 8792
	{		{
	"$schema": "https://json-schema.org/draft/2020-12/schema",		"$schema": "https://json-schema.org/draft/2020-12/schema",
	"title": "An RFC7807 problem object",		"title": "An RFC7807 problem object",
	"type": "object",		"type": "object",
	"properties": {		"properties": {
	"type": {		"type": {
	"type": "string",		"type": "string",
	skipping to change at line 727 ¶		skipping to change at page 16, line 23 ¶
	& element detail { xsd:string }?		& element detail { xsd:string }?
	& element status { xsd:positiveInteger }?		& element status { xsd:positiveInteger }?
	& element instance { xsd:anyURI }? ),		& element instance { xsd:anyURI }? ),
	anyNsElement		anyNsElement
	}		}
	anyNsElement =		anyNsElement =
	( element ns:* { anyNsElement | text }		( element ns:* { anyNsElement | text }
	| attribute * { text })*		| attribute * { text })*
	Note that this schema is only intended as documentation, and not as a		Note that this schema is only intended as documentation and not as a
	normative schema that captures all constraints of the XML format. It		normative schema that captures all constraints of the XML format. It
	is possible to use other XML schema languages to define a similar set		is possible to use other XML schema languages to define a similar set
	of constraints (depending on the features of the chosen schema		of constraints (depending on the features of the chosen schema
	language).		language).
	The media type for this format is "application/problem+xml".		The media type for this format is "application/problem+xml".
	Extension arrays and objects are serialized into the XML format by		Extension arrays and objects are serialized into the XML format by
	considering an element containing a child or children to represent an		considering an element containing a child or children to represent an
	object, except for elements that contain only child element(s) named		object, except for elements containing only one or more child
	'i', which are considered arrays. For example, the example above		elements named "i", which are considered arrays. For example, the
	appears in XML as follows:		example above appears in XML as follows:
	HTTP/1.1 403 Forbidden		HTTP/1.1 403 Forbidden
	Content-Type: application/problem+xml		Content-Type: application/problem+xml
	Content-Language: en		Content-Language: en
	<?xml version="1.0" encoding="UTF-8"?>		<?xml version="1.0" encoding="UTF-8"?>
	<problem xmlns="urn:ietf:rfc:7807">		<problem xmlns="urn:ietf:rfc:7807">
	<type>https://example.com/probs/out-of-credit</type>		<type>https://example.com/probs/out-of-credit</type>
	<title>You do not have enough credit.</title>		<title>You do not have enough credit.</title>
	<detail>Your current balance is 30, but that costs 50.</detail>		<detail>Your current balance is 30, but that costs 50.</detail>
	skipping to change at line 757 ¶		skipping to change at page 17, line 4 ¶
	<type>https://example.com/probs/out-of-credit</type>		<type>https://example.com/probs/out-of-credit</type>
	<title>You do not have enough credit.</title>		<title>You do not have enough credit.</title>
	<detail>Your current balance is 30, but that costs 50.</detail>		<detail>Your current balance is 30, but that costs 50.</detail>
	<instance>https://example.net/account/12345/msgs/abc</instance>		<instance>https://example.net/account/12345/msgs/abc</instance>
	<balance>30</balance>		<balance>30</balance>
	<accounts>		<accounts>
	<i>https://example.net/account/12345</i>		<i>https://example.net/account/12345</i>
	<i>https://example.net/account/67890</i>		<i>https://example.net/account/67890</i>
	</accounts>		</accounts>
	</problem>		</problem>
	This format uses an XML namespace, primarily to allow embedding it		This format uses an XML namespace, primarily to allow embedding it
	into other XML-based formats; it does not imply that it can or should		into other XML-based formats; it does not imply that it can or should
	be extended with elements or attributes in other namespaces. The		be extended with elements or attributes in other namespaces. The
	RELAX NG schema explicitly only allows elements from the one		RELAX NG schema explicitly only allows elements from the one
	namespace used in the XML format. Any extension arrays and objects		namespace used in the XML format. Any extension arrays and objects
	MUST be serialized into XML markup using only that namespace.		MUST be serialized into XML markup using only that namespace.
	When using the XML format, it is possible to embed an XML processing		When using the XML format, it is possible to embed an XML processing
	instruction in the XML that instructs clients to transform the XML,		instruction in the XML that instructs clients to transform the XML,
	using the referenced XSLT code [XSLT]. If this code is transforming		using the referenced XSL Transformations (XSLT) code [XSLT]. If this
	the XML into (X)HTML, then it is possible to serve the XML format,		code is transforming the XML into (X)HTML, then it is possible to
	and yet have clients capable of performing the transformation display		serve the XML format, and yet have clients capable of performing the
	human-friendly (X)HTML that is rendered and displayed at the client.		transformation display human-friendly (X)HTML that is rendered and
	Note that when using this method, it is advisable to use XSLT 1.0 in		displayed at the client. Note that when using this method, it is
	order to maximize the number of clients capable of executing the XSLT		advisable to use XSLT 1.0 in order to maximize the number of clients
	code.		capable of executing the XSLT code.
	Appendix C. Using Problem Details with Other Formats		Appendix C. Using Problem Details with Other Formats
	In some situations, it can be advantageous to embed problem details		In some situations, it can be advantageous to embed problem details
	in formats other than those described here. For example, an API that		in formats other than those described here. For example, an API that
	uses HTML [HTML5] might want to also use HTML for expressing its		uses HTML [HTML5] might want to also use HTML for expressing its
	problem details.		problem details.
	Problem details can be embedded in other formats either by		Problem details can be embedded in other formats either by
	encapsulating one of the existing serializations (JSON or XML) into		encapsulating one of the existing serializations (JSON or XML) into
	skipping to change at line 802 ¶		skipping to change at page 17, line 48 ¶
	"type": "https://example.com/probs/out-of-credit",		"type": "https://example.com/probs/out-of-credit",
	"title": "You do not have enough credit.",		"title": "You do not have enough credit.",
	"detail": "Your current balance is 30, but that costs 50.",		"detail": "Your current balance is 30, but that costs 50.",
	"instance": "/account/12345/msgs/abc",		"instance": "/account/12345/msgs/abc",
	"balance": 30,		"balance": 30,
	"accounts": ["/account/12345",		"accounts": ["/account/12345",
	"/account/67890"]		"/account/67890"]
	}		}
	</script>		</script>
	or by defining a mapping into RDFa [RDFA].		or by defining a mapping into a Resource Description Framework in
			Attributes (RDFa) [RDFA].
	This specification does not make specific recommendations regarding		This specification does not make specific recommendations regarding
	embedding problem details in other formats; the appropriate way to		embedding problem details in other formats; the appropriate way to
	embed them depends both upon the format in use and application of		embed them depends both upon the format in use and application of
	that format.		that format.
	Appendix D. Changes from RFC 7807		Appendix D. Changes from RFC 7807
	This revision has made the following changes:		This revision has made the following changes:
End of changes. 52 change blocks.
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