An Encoding Parameter for HTTP Basic Authentication

The "Basic" authentication scheme defined in RFC 2617 does not properly define how to treat non-ASCII characters. This has lead to a situation where user agent implementations disagree, and servers make different assumptions based on the locales they are running in. There is little interoperability for characters in the ISO-8859-1 character set, and even less interoperability for any characters beyond that.¶

This document defines a backwards-compatible extension to "Basic", specifying the server's character encoding expectation, using a new authentication scheme parameter.¶

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The "Basic" authentication scheme defined in Section 2 of [RFC2617] does not properly define how to treat non-ASCII characters ([USASCII]): it uses the Base64 ([RFC4648], Section 4) encoding of the concatenation of username, separator character, and password without stating which character encoding to use.¶

This has lead to a situation where user agent implementations disagree, and servers make different assumptions based on the locales they are running in. There is little interoperability for characters in the ISO-8859-1 character set ([ISO-8859-1]), and even less interoperability for any characters beyond that.¶

This document defines a backwards-compatible extension to "Basic", specifying the server's character encoding expect I ↓ation, using a new auth-param as defined in Section 1.2 of [RFC2617].¶

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

In challenges, servers MAY use the "encoding" authentication parameter (case-insensitive) to express the character encoding they expect the user agent to use.¶

The only allowed value is "UTF-8", to be matched case-insensitively (see [RFC2978], Section 2.3), indicating that the server expects the UTF-8 character encoding to be used ([RFC3629]).¶

Other values are reserved for future use.¶

For credentials sent by the user agent, the "encoding" parameter is reserved for future use and MUST NOT be sent.¶

The reason for this is that the information that could be included does not seem to be useful to the server, but the additional complexity of parsing and processing the additional parameter might make this extension harder to deploy.¶

In the example below, the server prompts for authentication in the "foo" realm, using Basic authentication, with a preference for the UTF-8 character encoding:

WWW-Authenticate: Basic realm="foo", encoding="UTF-8"

Note that the parameter value can be either a token or a quoted string; in this case the server chose to use the quoted-string notation.

This document does not introduce any new security considerations beyond those defined for the "Basic" authentication scheme ([RFC2617], Section 4), and those applicable to the handling of UTF-8 ([RFC3629], Section 10).¶

There are no IANA Considerations related to this specification.¶

The internationalisation problem 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.¶

Thanks to Martin Thomson for providing feedback on this document.¶