Basic access authentication
HTTP Basic authentication (BA) implementation is the simplest technique for enforcing access controls to web resources because it doesn't require cookies, session identifier and login pages. Rather, HTTP Basic authentication uses static, standard HTTP headers which means that no handshakes have to be done in anticipation.
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. Basic Authentication is, therefore, typically used over HTTPS.
Because the BA header has to be sent with 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.
While HTTP does not provide a method for web server to instruct the browser to "log out" the user (forget cached credentials), there are a number of workarounds using specific features in various browsers. One of them is redirecting the user to a URL on the same domain containing credentials that are intentionally incorrect:
When the server wants the user agent to authenticate itself towards the server, it can send a request for authentication.
The WWW-Authenticate header for basic authentication (used most often) is constructed as following:
WWW-Authenticate: Basic realm="insert realm"
When the user agent wants to send the server authentication credentials it may use the Authorization header.
The Authorization header is constructed as follows:
- Username and password are combined into a string "username:password"
- The resulting string is then encoded using the RFC2045-MIME variant of Base64, except not limited to 76 char/line
- The authorization method and a space i.e. "Basic " is then put before the encoded string.
For example, if the user agent uses 'Aladdin' as the username and 'open sesame' as the password then the header is formed as follows:
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
References and notes
- "Basic Authentication". Microsoft. 2005. Retrieved March 15, 2013.
- "Is there a browser equivalent to IE's ClearAuthenticationCache?". StackOverflow. Retrieved March 15, 2013.
- "IDM_CLEARAUTHENTICATIONCACHE command identifier". Microsoft. Retrieved March 15, 2013.