code: def authentication_validation(username, password, access_token):
      '''
      Only accept one form of authentication.
      '''
      if bool(username) is not bool(password):
          raise Exception("Basic authentication requires a username AND"
                          " password.")
      if (username and access_token) or (password and access_token):
          raise Exception("Cannot use both Basic Authentication and"
                          " OAuth2.0. Please use only one authentication"
                          " method."f authentication_validation(username, password, access_token):
      '''
      Only accept one form of authentication.
      '''
      if bool(username) is not bool(password):
          raise Exception("Basic authentication requires a username AND"
                          " password.")
      if (username and access_token) or (password and access_token):
          raise Exception("Cannot use both Basic Authentication and"
                          " OAuth2.0. Please use only one authentication"
                          " method.")
docs: Only accept one form of authentication.