HTTPAuth Working Group                                        J. Reschke
Internet-Draft                                                greenbytes
Obsoletes: 2617 (if approved)                           December 2, 2014
Intended status: Standards Track
Expires: June 5, 2015

                 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.

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

   Discussion of this draft takes place on the HTTPAuth working group
   mailing list (, which is archived at <http://>.

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

   The changes in this draft are summarized in Appendix C.4.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 5, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

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   This document may contain material from IETF Documents or IETF
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  4
       1.1.1.  Syntax Notation  . . . . . . . . . . . . . . . . . . .  4
   2.  The 'Basic' Authentication Scheme  . . . . . . . . . . . . . .  4
     2.1.  The 'charset' auth-param . . . . . . . . . . . . . . . . .  6
     2.2.  Re-using Credentials . . . . . . . . . . . . . . . . . . .  8
   3.  Internationalization Considerations  . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Changes from RFC 2617 . . . . . . . . . . . . . . . . 12
   Appendix B.  Deployment Considerations for the 'charset'
                Parameter . . . . . . . . . . . . . . . . . . . . . . 12
     B.1.  User Agents  . . . . . . . . . . . . . . . . . . . . . . . 12
     B.2.  Origin Servers . . . . . . . . . . . . . . . . . . . . . . 13
     B.3.  Why not simply switch the default encoding to UTF-8? . . . 13
   Appendix C.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 13
     C.1.  Since RFC 2617 . . . . . . . . . . . . . . . . . . . . . . 13
     C.2.  Since draft-ietf-httpauth-basicauth-update-00  . . . . . . 13
     C.3.  Since draft-ietf-httpauth-basicauth-update-01  . . . . . . 14
     C.4.  Since draft-ietf-httpauth-basicauth-update-02  . . . . . . 14

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1.  Introduction

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

   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.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

1.1.1.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234].

   The terms protection space and realm are defined in Section 2.2 of

   The terms (character) repertoire and character encoding scheme are
   defined in Section 2 of [RFC6365].

2.  The 'Basic' Authentication Scheme

   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.

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   The "Basic" authentication scheme utilizes the Authentication
   Framework as follows:

   In challenges:

   o  the scheme name is "Basic"

   o  the authentication parameter "realm" is REQUIRED ([RFC7235],
      Section 2.2)

   o  the authentication parameter "charset" is OPTIONAL (see
      Section 2.1)

   o  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-

   For credentials, the "token-68" syntax defined in Section 2.2 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 userid and password from the user,

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   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 ([USASCII]).

   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 to US-ASCII (mapping any US-ASCII character
   to a single octet matching the US-ASCII character code).

   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==

2.1.  The 'charset' auth-param

   In challenges, servers can use the "charset" authentication parameter
   to indicate the character encoding scheme they expect the user agent
   to use when generating "user-pass" (a sequence of octets).  This
   information is purely advisory.

   The only allowed value is "UTF-8", to be matched case-insensitively
   (see [RFC2978], Section 2.3).  It indicates that the server expects
   character data to be converted to Unicode Normalization Form C
   ("NFC", see Section 3 of [RFC5198]) and to be encoded into octets
   using the UTF-8 character encoding scheme ([RFC3629]).

   For the userid, recipients MUST support all characters defined in the
   "UsernameCasePreserved" profile defined in in Section 3.3 of

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   [PRECIS], with the exception of the colon (":") character.

   For the password, recipients MUST support all characters defined in
   the "Password" profile defined in in Section 4.2 of [PRECIS].

   Other values are reserved for future use.

      Note: The 'charset' is only defined on challenges, as "Basic" uses
      a single token for credentials ('token68' syntax), thus the
      credentials syntax isn't extensible.

      Note: The name 'charset' has been chosen for consistency with
      Section 2.1.1 of [RFC2831].  A better name would have been
      'accept-charset', as it is not about the message it appears in,
      but the server's expectation.

   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 scheme:

      WWW-Authenticate: Basic realm="foo", charset="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

   The user's name is "test", and the password is the string "123"
   followed by the Unicode character U+00A3 (POUND SIGN).  Using the
   character encoding scheme UTF-8, the user-pass becomes:

      '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==

   Or, for proxy authentication:

      Proxy-Authorization: Basic dGVzdDoxMjPCow==

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2.2.  Re-using Credentials

   Given the absolute URI ([RFC3986], Section 4.3) of an authenticated
   request, the authentication scope of that request is obtained by
   removing all characters after the last slash ("/") character.  A
   client SHOULD assume that resources identified by URIs with a prefix-
   match of the authentication scope are also within the protection
   space specified by the realm value of the that authenticated request.

   A client MAY preemptively send the corresponding Authorization header
   field with requests for resources in that space without receipt of
   another challenge from the server.  Similarly, when a client sends a
   request to a proxy, it may reuse a userid and password in the Proxy-
   Authorization header field without receiving another challenge from
   the proxy server.

   For example, given an authenticated request to:

   ...requests to the URIs below could use the known credentials:

   ...while the URIs

   would be considered to be outside the authentication scope.

   Note that a URI can be part of multiple authentication scopes (such
   as "" and "").  This
   specification does not define which of these should be treated with
   higher priority.

3.  Internationalization Considerations

   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.  Senders 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,

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   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.

4.  Security Considerations

   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 essentially cleartext transmission of the user's password over
   the physical network.  Many other authentication schemes address this

   Because Basic authentication involves the cleartext transmission of
   passwords it SHOULD NOT be used (without enhancements) 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,

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   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

5.  IANA Considerations

   IANA maintains the registry of HTTP Authentication Schemes
   ([RFC7235]) at <>.

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

6.  Acknowledgements

   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

   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
   <> and also the
   more recent <>).
   It was Andrew Clover's idea to address it using a new auth-param.

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

7.  References

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7.1.  Normative References

   [DIGEST]      Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
                 Digest Access Authentication",
                 draft-ietf-httpauth-digest-08 (work in progress),
                 August 2014.

   [PRECIS]      Saint-Andre, P. and A. Melnikov, "Preparation,
                 Enforcement, and Comparison of Internationalized
                 Strings Representing Usernames and Passwords",
                 draft-ietf-precis-saslprepbis-11 (work in progress),
                 November 2014.

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2978]     Freed, N. and J. Postel, "IANA Charset Registration
                 Procedures", BCP 19, RFC 2978, October 2000.

   [RFC3629]     Yergeau, F., "UTF-8, a transformation format of ISO
                 10646", STD 63, RFC 3629, November 2003.

   [RFC3986]     Berners-Lee, T., Fielding, R., and L. Masinter,
                 "Uniform Resource Identifier (URI): Generic Syntax",
                 STD 66, RFC 3986, January 2005.

   [RFC4648]     Josefsson, S., "The Base16, Base32, and Base64 Data
                 Encodings", RFC 4648, October 2006.

   [RFC5198]     Klensin, J. and M. Padlipsky, "Unicode Format for
                 Network Interchange", RFC 5198, March 2008.

   [RFC5234]     Crocker, D., Ed. and P. Overell, "Augmented BNF for
                 Syntax Specifications: ABNF", STD 68, RFC 5234,
                 January 2008.

   [RFC6365]     Hoffman, P. and J. Klensin, "Terminology Used in
                 Internationalization in the IETF", BCP 166, RFC 6365,
                 September 2011.

   [RFC7235]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
                 Transfer Protocol (HTTP/1.1): Authentication",
                 RFC 7235, June 2014.

   [USASCII]     American National Standards Institute, "Coded Character
                 Set -- 7-bit American Standard Code for Information
                 Interchange", ANSI X3.4, 1986.

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7.2.  Informative References

   [ISO-8859-1]  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.

   [RFC2617]     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.

   [RFC2831]     Leach, P. and C. Newman, "Using Digest Authentication
                 as a SASL Mechanism", RFC 2831, May 2000.

   [RFC5246]     Dierks, T. and E. Rescorla, "The Transport Layer
                 Security (TLS) Protocol Version 1.2", RFC 5246,
                 August 2008.

   [RFC6973]     Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
                 Morris, J., Hansen, M., and R. Smith, "Privacy
                 Considerations for Internet Protocols", RFC 6973,
                 July 2013.

   [RFC7231]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
                 Transfer Protocol (HTTP/1.1): Semantics and Content",
                 RFC 7231, June 2014.

Appendix A.  Changes from RFC 2617

   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.

Appendix B.  Deployment Considerations for the 'charset' Parameter

B.1.  User Agents

   User agents not implementing 'charset' will continue to work as
   before, ignoring the new parameter.

   User agents which already default to the UTF-8 encoding implement
   'charset' by definition.

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

B.2.  Origin Servers

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

   Origin servers that need to support non-US-ASCII characters, but
   cannot use the UTF-8 character encoding scheme will not be affected;
   they will continue to function as well or as badly as before.

   Finally, origin servers that need to support non-US-ASCII characters
   and can use the UTF-8 character encoding scheme 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).

B.3.  Why not simply switch the default encoding to UTF-8?

   There are sites in use today that default to a local character
   encoding scheme, such as ISO-8859-1 ([ISO-8859-1]), and expect user
   agents to use that encoding.  Authentication on these sites will stop
   to work if the user agent switches to a different encoding, such as

   Note that sites might even inspect the User-Agent header field
   ([RFC7231], Section 5.5.3) to decide what character encoding scheme
   to expect from the client.  Therefore they might support UTF-8 for
   some user agents, but default to something else for others.  User
   agents in the latter group will have to continue to do what they do
   today until the majority of these servers have been upgraded to
   always use UTF-8.

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

C.1.  Since RFC 2617

   This draft acts as a baseline for tracking subsequent changes to the
   specification.  As such, it extracts the definition of "Basic", plus
   the related Security Considerations, and also adds the IANA
   registration of the scheme.  Changes to the actual definition will be
   made in subsequent drafts.

C.2.  Since draft-ietf-httpauth-basicauth-update-00

   Fixed Base64 reference to point to an actual definition of Base64.

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   Update HTTPbis and Digest references.

   Note that this spec, together with HTTPbis P7 and the Digest update,
   obsoletes RFC 2617.

   Rewrote text about authentication parameters and their extensibility.

   Pulled in the definition of the "charset" parameter.

   Removed a misleading statement about userids potentially being case-
   sensitive, as the same is true for passwords.

   Added TODOs with respect to path matching, and colons in userids.

C.3.  Since draft-ietf-httpauth-basicauth-update-01

   Minor improvements on Security Considerations.

   Update Digest reference.

   Rewrite scheme definition as algorithm rather than pseudo-ABNF.

   Add a note about colons in userid.

   Attempt to explain authentication scopes.

C.4.  Since draft-ietf-httpauth-basicauth-update-02

   Reference draft-ietf-precis-saslprepbis for the set of characters
   that need to be supported in userids and passwords.

Author's Address

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


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