Creates a new Auth of type type with the information from msg
and auth_header.
This is called by [class@Session]; you will normally not create auths yourself.
| type |
the type of auth to create (a subtype of Auth) |
| msg |
the Message the auth is being created for |
| auth_header |
the WWW-Authenticate/Proxy-Authenticate header |
|
the new Auth, or null if it could not be created |