code: public void setIdentitySource(java.util.Collection<String> identitySource) {
          if (identitySource == null) {
              this.identitySource = null;
              return;
          }
  
          this.identitySource = new java.util.ArrayList<String>(identitySource);
      }
docs: <p>
  The identity source for which authorization is requested.
  </p>
  <p>
  For the REQUEST authorizer, this is required when authorization caching is enabled. The value is a
  comma-separated string of one or more mapping expressions of the specified request parameters. For example, if an
  Auth header and a Name query string parameters are defined as identity sources, this value is
  method.request.header.Auth, method.request.querystring.Name. These parameters will be used to derive the
  authorization caching key and to perform runtime validation of the REQUEST authorizer by verifying all of the
  identity-related request parameters are present, not null, and non-empty. Only when this is true does the
  authorizer invoke the authorizer Lambda function, otherwise, it returns a 401 Unauthorized response without
  calling the Lambda function. The valid value is a string of comma-separated mapping expressions of the specified
  request parameters. When the authorization caching is not enabled, this property is optional.
  </p>
  
  @param identitySource
  The identity source for which authorization is requested.</p>
  <p>
  For the REQUEST authorizer, this is required when authorization caching is enabled. The value is a
  comma-separated string of one or more mapping expressions of the specified request parameters. For
  example, if an Auth header and a Name query string parameters are defined as identity sources, this value
  is method.request.header.Auth, method.request.querystring.Name. These parameters will be used to derive
  the authorization caching key and to perform runtime validation of the REQUEST authorizer by verifying all
  of the identity-related request parameters are present, not null, and non-empty. Only when this is true
  does the authorizer invoke the authorizer Lambda function, otherwise, it returns a 401 Unauthorized
  response without calling the Lambda function. The valid value is a string of comma-separated mapping
  expressions of the specified request parameters. When the authorization caching is not enabled, this
  property is optional.