HTTP Basic authentication (BA) implementation is the simplest technique for enforcing access controls to web resources because it does not require cookies, session identifiers, or login pages; rather, HTTP Basic authentication uses standard fields in the HTTP header, removing the need for handshakes.
The BA mechanism provides no confidentiality protection for the transmitted credentials. They are merely encoded with Base64 in transit, but not encrypted or hashed in any way. Therefore, Basic Authentication is typically used in conjunction with HTTPS to provide confidentiality.
Because the BA field has to be sent in the header of each HTTP request, the web browser needs to cache credentials for a reasonable period of time to avoid constantly prompting the user for their username and password. Caching policy differs between browsers. Microsoft Internet Explorer by default caches them for 15 minutes.
When the server wants the user agent to authenticate itself towards the server, the server must respond appropriately to unauthenticated requests.
The WWW-Authenticate field for basic authentication is constructed as following:
WWW-Authenticate: Basic realm="User Visible Realm"
The server may choose to include the charset parameter from RFC 7617:
WWW-Authenticate: Basic realm="User Visible Realm", charset="UTF-8"
This parameter indicates that the server expects the client to use UTF-8 for encoding username and password (see below).
When the user agent wants to send authentication credentials to the server, it may use the Authorization field.
The Authorization field is constructed as follows:
For example, if the browser uses Aladdin as the username and OpenSesame as the password, then the field's value is the base64-encoding of Aladdin:OpenSesame, or QWxhZGRpbjpPcGVuU2VzYW1l. Then the Authorization header will appear as:
Authorization: Basic QWxhZGRpbjpPcGVuU2VzYW1l
A client may avoid a login prompt when accessing a basic access authentication by prepending
username:password@ to the hostname in the URL. For example, the following would access the page index.html at the web site www.example.com with the secure HTTPS protocol and provide the username Aladdin and the password OpenSesame credentials via basic authorization:
This has been deprecated by RFC 3986: Use of the format "user:password" in the userinfo field is deprecated. Some modern browsers thus no longer support URL encoding of basic access credentials. This prevents passwords from being sent and seen prominently in plain text, and also eliminates confusing URLs like
which would query the host example.com, not google.com.
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