Network Working GroupJ. Reschke
Updates: 2617 (if approved)January 25, 2012
Intended status: Standards Track
Expires: July 28, 2012

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.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on July 28, 2012.

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Editorial Note (To be removed by RFC Editor before publication)

Distribution of this document is unlimited. Although this is not a work item of the HTTPbis Working Group, comments should be sent to the Hypertext Transfer Protocol (HTTP) mailing list at, which may be joined by sending a message with subject "subscribe" to

Discussions of the HTTPbis Working Group are archived at <>.

XML versions, latest edits and the issues list for this document are available from <>.

 I  edit   (type: edit, status: open)
julian.reschke@greenbytes.de2010-08-11 Umbrella issue for editorial fixes/enhancements.
Associated changes in this document: 1, C.

1. Introduction

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].

2. Notational Conventions

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].

3. The 'encoding' auth-param

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.

4. Examples

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.

The user's name is "test", and his password is the string "123" followed by the Unicode character U+00A3 (POUND SIGN). Following Section 1.2 of [RFC2617], but using the character encoding UTF-8, the user-pass, converted to a sequence of octets, is:

 't' 'e' 's' 't' ':' '1' '2' '3' pound
 74  65  73  74  3A  31  32  33  C2  A3  

Encoding this octet sequence in Base64 ([RFC4648], Section 4) yields:


Thus the Authorization header field would be:

  Authorization: Basic dGVzdDoxMjPCow==

5. Security Considerations

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).

6. IANA Considerations

There are no IANA Considerations related to this specification.

7. Acknowledgements

The internationalisation problem has been reported as a Mozilla bug back in the year 2000 (see <> and also the more recent <>). It was Andrew Clover's idea to address it using a new auth-param.

Thanks to Martin Thomson for providing feedback on this document.

8. References

8.1. Normative References

International Organization for Standardization, “Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1”, ISO/IEC 8859-1:1998, 1998.
Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.
Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication”, RFC 2617, June 1999.
Freed, N. and J. Postel, “IANA Charset Registration Procedures”, BCP 19, RFC 2978, October 2000.
Yergeau, F., “UTF-8, a transformation format of ISO 10646”, STD 63, RFC 3629, November 2003.
American National Standards Institute, “Coded Character Set -- 7-bit American Standard Code for Information Interchange”, ANSI X3.4, 1986.

8.2. Informative References

Josefsson, S., “The Base16, Base32, and Base64 Data Encodings”, RFC 4648, October 2006.
van Kesteren, A., “XMLHttpRequest Level 2”, W3C Working Draft WD-XMLHttpRequest2-20110816, August 2011, <>.
Latest version available at <>.

Appendix A. Deployment Considerations

A.1. User Agents

User agents not implementing this specifications should continue to work as before, ignoring the new parameter.

User agents which already default to the UTF-8 encoding already implement this specification by definition. I Note that some user agents already have different defaults depending on whether the request originates from page navigation as opposed to a script-driven request using XMLHttpRequest [XHR].

Other user agents can keep their default behavior, and switch to UTF-8 when seeing the new parameter.

A.1.1. Alternative approach

On the other hand, the strategy below may already improve the user-visible behavior today:

  • In the first authentication request, choose the character encoding based on the user's credentials: if they do not need any characters outside the ISO-8859-1 character set, default to ISO-8859-1, otherwise use UTF-8.
  • If the first attempt failed and the encoding used was ISO-8859-1, retry once with UTF-8 encoding instead.

Note that there's a risk if the site blocks an account after multiple login failures (for instance, when it doesn't reset the counter after a successful login).

A.2. Origin Servers

Origin servers that do not support non-ASCII characters in credentials do not require any changes.

Origin servers that need to support non-ASCII characters, but can't use the UTF-8 encoding will not be affected; they will continue to function as well as before.

Finally, origin servers that need to support non-ASCII characters and can use the UTF-8 encoding can opt in as described above. In the worst case, they'll continue to see either broken credentials or no credentials at all (depending on how legacy clients handle characters they can not encode).

Appendix B. FAQ (to be removed by RFC Editor before publication)

B.1. Why not simply switch the default encoding to UTF-8?

There are sites in use today that default to a locale encoding, such as ISO-8859-1, and expect user agents to use that encoding. These sites will break if the user agent uses a different encoding, such as UTF-8.

B.2. What about Digest?

Although the solution proposed in this document may be applicable to "Digest" as well, any attempt to update this scheme may be an uphill battle hard to win.

B.3. Will existing UAs ignore the parameter?

Appendix C. Change Log (to be removed by RFC Editor before publication)

C.1. Since draft-reschke-basicauth-enc-00

Add and close issues "credparam" and "paramcase". Rewrite the deployment considerations.

C.2. Since draft-reschke-basicauth-enc-01

Note more recent Mozilla bugzilla entry; add behavior of existing UAs to FAQ (with pointer to test cases).


C.3. Since draft-reschke-basicauth-enc-02

Add and resolve issue "xhrutf8".

Author's Address

Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155