title: AWS Lambda API gateway with Cognito - how to use IdentityId to access and update UserPool attributes?
body: <p>OK I am now days into this and have made significant progress but am still completely stumped about the fundamentals.</p>
  
  <p>My application uses Cognito User Pools for creating and managing users - these are identified on S3 it seems by their IdentityId. Each of my users has their own S3 folder, and AWS automatically gives them a folder name that is equal to the user's IdentityId.</p>
  
  <p>I need to relate the IdentityId to the other Cognito user information but cannot work out how.</p>
  
  <p>The key thing I need is to be able to identify the username plus other cognito user attributes for a given IdentityId - and it's insanely hard.</p>
  
  <p>So the first battle was to work out how to get the IdentityId when a Cognito user does a request via the AWS API Gateway.  Finally I got that worked out, and now I have a Cognito user, who does a request to the API Gateway, and my Lambda function behind that now has the IdentityId.  That bit works.</p>
  
  <p>But I am completely stumped as to how to now access the Cognito user's information that is stored in the user pool.  I can't find any clear information, and certainly no code, that shows how to use the IdentityId to get the Cognito user's attributes, username etc.</p>
  
  <p>It appears that if I use a "Cognito user pool" to authorize my method in API Gateway, then the body mapping template can be used to put Cognito User information such as the sub and the username and email address into the context, BUT I do NOT get the IdentityId. </p>
  
  <p>BUT if I use the <code>AWS_IAM</code> to authorize my method in the API gateway then the body mapping template does the inverse - it gives me the IdentityId but not the Cognito user fields such as sub and username and email.</p>
  
  <p>It's driving me crazy - how can I get the IdentityId and all the Cognito users fields and attributes together into one data structure? The fact that I seem to be only able to get one or the other just makes no sense.</p>