title: Cognito USER_SRP_AUTHENTICATION
body: <p>In the AWS Cognito docs, <a href="http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/CognitoIdentityServiceProvider.html#initiateAuth-property" rel="noreferrer">http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/CognitoIdentityServiceProvider.html#initiateAuth-property</a></p>
  
  <p>One of the supported Authentication flow is USER_SRP_AUTH. When I call the initiateAuth(), I get</p>
  
  <p><strong>InvalidParameterException: Missing required parameter SRP_A error.</strong></p>
  
  <p>The doc is silent about how to get/generate this SRP_A that the method requires. Where can I find how to use this auth flow?</p>
  
  <p>Thanks in advance!</p>