MINOR: http_fetch: Add sample fetches to get auth method/user/pass

Now, following sample fetches may be used to get information about
authentication:

 * http_auth_type : returns the auth method as supplied in Authorization header
 * http_auth_user : returns the auth user as supplied in Authorization header
 * http_auth_pass : returns the auth pass as supplied in Authorization header

Only Basic authentication is supported.
2 files changed