code: def validate_auth_mechanism(option, value):
      
      # CRAM-MD5 is for server testing only. Undocumented,
      # unsupported, may be removed at any time. You have
      # been warned.
      if value not in MECHANISMS and value != 'CRAM-MD5':
          raise ValueError("%s must be in %s" % (option, tuple(MECHANISMS)))
      return value
docs: Validate the authMechanism URI option.