SITUATION
You have a few of options to fully customize the authentication handling:
Utilize setWillSendRequestForAuthenticationChallengeBlock: and setAuthenticationAgainstProtectionSpaceBlock: from class AFURLConnectionOperation and set corresponding blocks where you can tailor the mechanism you require.
The headers contain documentation.
Override connection:willSendRequestForAuthenticationChallenge: in a subclass of AFURLConnectionOperation. This will effectively override the complete authentication mechanism setup in AFNetworking.
Note, that you cannot disable the "server validates client identity" authentication challenge -- this is part of the server. You MUST provide the correct credentials for the requested authentication method.