The 'Basic' HTTP Authentication Scheme

This document defines the "Basic" Hypertext Transfer Protocol (HTTP) Authentication Scheme, which transmits credentials as userid/password pairs, obfuscated by the use of Base64 encoding.¶

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This document defines the "Basic" Hypertext Transfer Protocol (HTTP) Authentication Scheme, which transmits credentials as userid/password pairs, obfuscated by the use of Base64 encoding (HTTP authentication schemes are defined in [RFC7235]).¶

This scheme is not considered to be a secure method of user authentication unless used in conjunction with some external secure system such as TLS (Transport Layer Security, [RFC5246]), as the user name and password are passed over the network as cleartext.¶

The "Basic" scheme previously was defined in Section 2 of [RFC2617]. This document updates the definition, and also addresses internationalization issues by introducing the "charset" authentication parameter (Section 2.1).¶

Other documents updating RFC 2617 are "Hypertext Transfer Protocol (HTTP/1.1): Authentication" ([RFC7235], defining the authentication framework) and "HTTP Digest Access Authentication" ([DIGEST], updating the definition of the '"Digest" authentication scheme). Taken together, these three documents obsolete RFC 2617.¶

The "Basic" authentication scheme is based on the model that the client needs to authenticate itself with a user-ID and a password for each protection space ("realm"). The realm value is an opaque string which can only be compared for equality with other realms on that server. The server will service the request only if it can validate the user-ID and password for the protection space applying to the requested resource.¶

In challenges: ¶

• the scheme name is "Basic"
• the authentication parameter "realm" is REQUIRED ([RFC7235], Section 2.2)
• the authentication parameter "charset" is OPTIONAL (see Section 2.1)
• no other authentication parameters are defined — unknown parameters MUST be ignored by recipients, and new parameters can only be defined by revising this specification

Note that both scheme and parameter names are matched case-insensitively.¶

For credentials, the "token68" syntax defined in Section 2.1 of [RFC7235] is used. The value is computed based on user-id and password as defined below.¶

Upon receipt of a request for a URI within the protection space that lacks credentials, the server can reply with a challenge using the 401 (Unauthorized) status code ([RFC7235], Section 3.1) and the WWW-Authenticate header field ([RFC7235], Section 4.1).¶

For instance:

HTTP/1.1 401 Unauthorized
Date: Mon, 04 Feb 2014 16:50:53 GMT
WWW-Authenticate: Basic realm="WallyWorld"

...where "WallyWorld" is the string assigned by the server to identify the protection space.

A proxy can respond with a similar challenge using the 407 (Proxy Authentication Required) status code ([RFC7235], Section 3.2) and the Proxy-Authenticate header field ([RFC7235], Section 4.3).¶

To receive authorization, the client ¶

1. obtains the userid and password from the user,
2. constructs the user-pass by concatenating userid, a single colon (":") character, and the password,
3. encodes the user-pass into an octet sequence (see below for a discussion of character encoding schemes),
4. and obtains the basic-credentials by encoding this octet sequence using base64 ([RFC4648], Section 4) into a sequence of US-ASCII characters ([RFC0020]).

The original definition of this authentication scheme failed to specify the character encoding scheme used to convert the user-pass into an octet sequence. In practice, most implementations chose either a local-specific encoding such as ISO-8859-1 ([ISO-8859-1]), or UTF-8 ([RFC3629]). For backwards compatibility reasons, this specification continues to leave the default encoding undefined, as long as it is compatible with US-ASCII (mapping any US-ASCII character to a single octet matching the US-ASCII character code).¶

The userid and password MUST NOT contain any control characters (see "CTL" in Appendix B.1 of [RFC5234]).¶

Furthermore, a userid containing a colon character is invalid, as recipients will split the user-pass at the first occurence of a colon character. Note that many user agents however will accept a colon in userid, thereby producing a user-pass string that recipients will likely treat in a way not intended by the user.¶

If the user agent wishes to send the userid "Aladdin" and password "open sesame", it would use the following header field:

Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

User names or passwords containing characters outside the US-ASCII character repertoire will cause interoperability issues, unless both communication partners agree on what character encoding scheme is to be used. Servers can use the new 'charset' parameter (Section 2.1) to indicate a preference of "UTF-8", increasing the probability that clients will switch to that encoding.¶

The "realm" parameter carries data that can be considered textual, however [RFC7235] does not define a way to reliably transport non-US-ASCII characters. This is a known issue that would need to be addressed in that specification.¶

The Basic authentication scheme is not a secure method of user authentication, nor does it in any way protect the entity, which is transmitted in cleartext across the physical network used as the carrier. HTTP does not prevent the addition of enhancements (such as schemes to use one-time passwords) to Basic authentication.¶

The most serious flaw in Basic authentication is that it results in the cleartext transmission of the user's password over the physical network. Many other authentication schemes address this problem.¶

Because Basic authentication involves the cleartext transmission of passwords it SHOULD NOT be used (without enhancements such as HTTPS [RFC2818]) to protect sensitive or valuable information.¶

A common use of Basic authentication is for identification purposes — requiring the user to provide a user name and password as a means of identification, for example, for purposes of gathering accurate usage statistics on a server. When used in this way it is tempting to think that there is no danger in its use if illicit access to the protected documents is not a major concern. This is only correct if the server issues both user name and password to the users and in particular does not allow the user to choose his or her own password. The danger arises because naive users frequently reuse a single password to avoid the task of maintaining multiple passwords.¶

If a server permits users to select their own passwords, then the threat is not only unauthorized access to documents on the server but also unauthorized access to any other resources on other systems that the user protects with the same password. Furthermore, in the server's password database, many of the passwords may also be users' passwords for other sites. The owner or administrator of such a system could therefore expose all users of the system to the risk of unauthorized access to all those sites if this information is not maintained in a secure fashion. This raises both security and privacy concerns ([RFC6973]). If the same username and password combination is in use to access other accounts, such as an email or health portal account, personal information could be exposed.¶

Basic Authentication is also vulnerable to spoofing by counterfeit servers. If a user can be led to believe that he is connecting to a host containing information protected by Basic authentication when, in fact, he is connecting to a hostile server or gateway, then the attacker can request a password, store it for later use, and feign an error. This type of attack is not possible with Digest Authentication. Server implementers SHOULD guard against the possibility of this sort of counterfeiting by gateways or CGI scripts. In particular it is very dangerous for a server to simply turn over a connection to a gateway. That gateway can then use the persistent connection mechanism to engage in multiple transactions with the client while impersonating the original server in a way that is not detectable by the client.¶

The use of the UTF-8 character encoding scheme introduces additional security considerations; see Section 10 of [RFC3629] for more information.¶

IANA maintains the registry of HTTP Authentication Schemes ([RFC7235]) at <http://www.iana.org/assignments/http-authschemes>.¶

The entry for the "Basic" Authentication Scheme shall be updated with a pointer to this specification.¶

This specification takes over the definition of the "Basic" HTTP Authentication Scheme, previously defined in RFC 2617. We thank John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for their work on that specification, from which significant amounts of text were borrowed. See Section 6 of [RFC2617] for further acknowledgements.¶

The internationalization problem with respect to the character encoding scheme used for user-pass has been reported as a Mozilla bug back in the year 2000 (see <https://bugzilla.mozilla.org/show_bug.cgi?id=41489> and also the more recent <https://bugzilla.mozilla.org/show_bug.cgi?id=656213>). It was Andrew Clover's idea to address it using a new auth-param.¶

We also thank the members of the HTTPAuth Working Group and other reviewers, namely Stephen Farrell, Bjoern Hoehrmann, Kari Hurtta, Amos Jeffries, Benjamin Kaduk, James Manger, Kathleen Moriarty, Yaron Sheffer, Michael Sweet, and Martin Thomson for feedback on this revision.¶

The scheme definition has been rewritten to be consistent with newer specifications such as [RFC7235].¶

The new authentication parameter "charset" has been added. It is purely advisory, so existing implementations do not need to change, unless they want to take advantage of the additional information which previously wasn't available.¶