Basic access authentication: Difference between revisions

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{{Short description|Access control method for the HTTP network communication protocol}}

{{HTTP}}

In the context of an [[HTTP]] transaction, '''basic access authentication''' is a method for an [[User Agent Profiling|HTTP user agent]] (e.g. a [[web browser]]) to provide a [[user name]] and [[password]] when making a request. In basic HTTP authentication, a request contains a header field in the form of <code>Authorization: Basic <&lt;credentials></code>, where <code><&lt;credentials></code> is the [[Base64]] encoding of ID and password joined by a single colon <code>:</code>.

It was originally implemented by [[Ari Luotonen]] at [[CERN]] in 1993<ref>{{cite mailing list |url=http://1997.webhistory.org/www.lists/www-talk.1993q3/0882.html |title=Announcing Access Authorization Documentation |date=10 September 2022 |access-date=7 February 2022 |mailing-list=[e-mail] |last=Luotonen |first=Ari}}</ref> and defined in the HTTP 1.0 specification in 1996.<ref>{{cite web |url=https://www.w3.org/Protocols/HTTP/1.0/spec.html#BasicAA |title=Hypertext Transfer Protocol -- HTTP/1.0 |date=19 February 1996 |website=www.w3.org |publisher=W3C |access-date=7 February 2022}}</ref>

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Because the BA field has to be sent in the header of each HTTP request, the web browser needs to [[Cache (computing)|cache]] credentials for a reasonable period of time to avoid constantly prompting the user for their username and password. Caching policy differs between browsers.

HTTP does not provide a method for a web server to instruct the client to "log out" the user. However, there are a number of methods to clear cached credentials in certain web browsers. One of them is redirecting the user to a URL on the same ___domain, using credentials that are intentionally incorrect. However, this behavior is inconsistent between various browsers and browser versions.<ref name=":0">{{cite web | url=https://stackoverflow.com/questions/31326/is-there-a-browser-equivalent-to-ies-clearauthenticationcache | title=Is there a browser equivalent to IE's ClearAuthenticationCache? | publisher=StackOverflow | access-date=March 15, 2013}}</ref>{{Better source needed|reason=The current source is user-generated and is insufficiently reliable ([[WP:NOTRS]]).|date=March 2025}} [[Internet Explorer|Microsoft Internet Explorer]] offers a dedicated JavaScript method to clear cached credentials:<ref>{{cite web | url=https://docs.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/platform-apis/hh801226(v=vs.85)#idmclearauthenticationcache | title=<code>IDM_CLEARAUTHENTICATIONCACHE</code> command identifier | publisher=Microsoft | access-date=March 15, 2013}}</ref>

<syntaxhighlight lang="html">

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=== Server side ===

When the server wants the user agent to authenticate itself towards the server after receiving an unauthenticated request, it must send a response with a ''HTTP 401 Unauthorized'' status line<ref>{{cite webIETF|titlerfc=RFC 1945 Section|section =11. |title=Access Authentication|url=https://tools.ietf.org/html/rfc1945#section-11|publisher=IETF|access-date=3 February 2017|page=46|date=May 1996 |publisher = [[Internet Engineering Task Force]]}}</ref> and a ''WWW-Authenticate'' header field.<ref>{{cite webIETF|urlrfc=http://tools.ietf.org/html/rfc1945#1945|section-=10.16|title=Hypertext Transfer Protocol -- HTTP/1.0|last1=Fielding|first1=Roy T.|last2=Berners-Lee|first2=Tim|first3=Frystyk|last3=Henrik|website=tools.ietf.org|author-link1=Roy Fielding|author-link2=Tim Berners-Lee|publisher = Internet Engineering Task Force}}</ref>

The ''WWW-Authenticate'' header field for basic authentication is constructed as following:

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When the user agent wants to send authentication credentials to the server, it may use the ''Authorization'' header field.

The ''Authorization'' header field is constructed as follows:<ref name="RFC7617">{{cite webIETF|urlrfc=https://tools.ietf.org/html/rfc7617#7617|section-=2.1|title=The 'Basic' HTTP Authentication Scheme|first=Julian|last=Reschke|websitepublisher =tools.ietf.org Internet Engineering Task Force}}</ref>

# The username and password are combined with a single colon ({{code|:}}). This means that the username itself cannot contain a colon.

# The resulting string is encoded into an octet sequence. The character set to use for this encoding is by default unspecified, as long as it is compatible with US-ASCII, but the server may suggest the use of UTF-8 by sending the ''charset'' parameter.<ref name="RFC7617" />

# The resulting string is encoded using a variant of Base64 (+/ and with padding).

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Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

</code>

<syntaxhighlight lang="python">

'Basic ' + base64.b64encode(f"{<clientid>}:{<client secret key>}".encode()).decode()

</syntaxhighlight>

== See also ==

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==External links==

*{{cite webIETF|title=RFC 7617 - The 'Basic' HTTP Authentication Scheme|urlrfc=https://datatracker.ietf.org/doc/html/rfc76177617|date=September 2015|publisher=[[Internet Engineering Task Force (IETF)|date=September 2015]]}}

[[Category:Hypertext Transfer Protocol]].

[[Category:Computer access control protocols]]