title: Verify user identity using cognito
body: <p>I'm creating a back-end service and I'm using AWS Cognito.
  Right now, I'm using my Developer Authenticated Identities.
  So, my user can login using my own system. This part is done.</p>
  
  <p>However, I'm having problems to authenticate the user after the login. Let's say that the user send me a request to access some private function of my API. How can I identify and authenticate this user?</p>
  
  <p>If I use facebook as login provider, I can fulfill the the http header with his Cognito ID and his facebook access token. Then, I can authenticate him, trying to get a Cognito Token using the function GetOpenIdTokenRequest.</p>
  
  <p>I will have something like </p>
  
  <pre><code>providerTokens.put("graph.facebook.com", "xxxxxxxxxxxx");
  tokenRequest.setLogins(providerTokens);
  
  AmazonCognitoIdentityClient identityClient = new AmazonCognitoIdentityClient();
          identityClient.setRegion(RegionUtils.getRegion(Configuration.REGION));
          GetOpenIdTokenResult tokenResp = identityClient.getOpenIdToken(tokenRequest);
  </code></pre>
  
  <p>However, I'm not using Facebook.</p>
  
  <p>So, I tried some something like this</p>
  
  <pre><code>providerTokens.put("customdeveloper.authentication.com", "xxxxxxxxxxxx");
  tokenRequest.setLogins(providerTokens);
  </code></pre>
  
  <p>Getting a error that my developer authentication is not a public provider.</p>
  
  <p>I'm quite confuse if I going on the right direction. I basically want to authenticate my user. Something similar to oauth2 where I receive a token can check the user identity. </p>
  
  <p>How is the right way of doing it using Cognito?</p>