Firstly, go into Cognito Identity provider (in the Cognito console) and make sure your provider "Authorize Scope" is suitable. For example if you clicked on the Google provider your Authorize scope might be "profile email openid". The scope will vary by provider, but whatever scope you are using, it must provide access to the users email.
When your user logs in with an external identity provider (lets say Facebook), Cognito negotiates with Facebook and then calls your Callback URL, which is set in the 'App Client Settings' part of the Cognito console. That Callback contains a parameter called 'code' - the parameter is set in the URL of the Callback made my Cognito. The code is an OAuth token.
Now you have an OAuth token in your client you need to POST that to the AWS Token Endpoint. The token endpoint returns three new tokens in the response; a JWT ID Token, a JWT Access Token and a refresh token. Take the "id_token" attribute from the endpoint response. Parse that id_token as a json string, and take the 'email' element. Now you should have the users email address.
Here is my working example in Java. This is a servlet that gets called by the Cognito Callback.
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
import com.nimbusds.jwt.SignedJWT;
import net.minidev.json.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.URL;
import java.net.URLConnection;
public class CognitoLandingServlet extends HttpServlet {
static final Logger LOG = LoggerFactory.getLogger(CognitoLandingServlet.class);
private static final long serialVersionUID = 1L;
public CognitoLandingServlet() {
super();
}
@Override
protected void doGet(final HttpServletRequest request, final HttpServletResponse response)
throws ServletException, IOException {
// Get the OpenID Connect (OAuth2) token passed back from the hosted Cognito
// Login Page
final String code = request.getParameter("code");
LOG.debug(String.format("Cognito OAuth2 code received from Cognito: %s.", code));
if (code != null) {
// do nothing, we have a code as expected
} else {
LOG.debug(String.format(
"Landing page requested without a Cognito code, the request probably didn't come from Cognito"));
// we dont have a token so redirect the user to the application sign in
// page
request.getRequestDispatcher("/signin").forward(request, response);
}
// Exchange the OIDC token for Cognito Access and ID JWT tokens using AWS
// Token
// Endpoint
// There does not appear to be a Java SDK to handle this :(
final String cognitoClientId = System.getProperty("CognitoClientId");
final String redirectUri = System.getProperty("CognitoCallBackUrl");
final String awsTokenEndpoint = System.getProperty("AwsTokenEndpoint");
final String jwt = swapOauthForJWT(cognitoClientId, code, redirectUri, awsTokenEndpoint);
// Complete the login using the JWT token string
loginWithJWT(jwt, request, response);
}
@Override
protected void doPost(final HttpServletRequest request, final HttpServletResponse response)
throws ServletException, IOException {
}
private void loginWithJWT(final String jwtString, final HttpServletRequest request,
final HttpServletResponse response) {
final JSONParser parser = new JSONParser();
SignedJWT signedIdJWT;
try {
// Take the id token
final JSONObject json = (JSONObject) parser.parse(jwtString);
final String idToken = (String) json.get("id_token");
// Access token is not currently used
// String accessToken = (String) json.get("access_token");
// Process the id token
signedIdJWT = SignedJWT.parse(idToken);
final String userId = signedIdJWT.getJWTClaimsSet().getSubject();
// Start NEW Session and start adding attributes
final HttpSession session = request.getSession(true);
session.setAttribute("userId", userId);
final String cognitoUsername = (String) signedIdJWT.getJWTClaimsSet()
.getClaim("cognito:username");
if (cognitoUsername != null) {
user.setUserName(cognitoUsername);
session.setAttribute("username", cognitoUsername);
}
final String email = (String) signedIdJWT.getJWTClaimsSet().getClaim("email");
if (email != null) {
user.setEmail(email);
session.setAttribute("email", email);
}
// Save the user to a database (code removed for stack overflow)
//request.getRequestDispatcher("/dashboard").forward(request, response);
response.sendRedirect("/dashboard");
LOG.info(
String.format("A user with userid %s and email %s successfully signed in", userId, email));
} catch (final java.text.ParseException e) {
LOG.error(
String.format("The JWT token could not be parsed by JOSE library. %s", e.getMessage()));
} catch (final ParseException e) {
LOG.error(String.format("The JWT token could not be parsed by JSON simple library. %s",
e.getMessage()));
} catch (final IOException e) {
LOG.error(String.format("Failed to request webpage at the end of the login process - io. %s",
e.getMessage()));
}
}
private String swapOauthForJWT(final String cognitoClientId, final String oauthCode,
final String redirectUri, final String awsTokenEndpoint) throws IOException {
// Build the URL to post to the AWS Token Endpoint
final String urlParameters = String.format(
"Content-Type=application/x-www-form-urlencoded&grant_type=authorization_code&client_id=%s&code=%s&redirect_uri=%s",
cognitoClientId, oauthCode, redirectUri);
LOG.debug(String.format("User is swapping OAuth token for a JWT using URL %s", urlParameters));
final URL url = new URL(awsTokenEndpoint);
final URLConnection conn = url.openConnection();
conn.setDoOutput(true);
final OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
writer.write(urlParameters);
writer.flush();
// Read the data returned from the AWS Token Endpoint
final BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
final StringBuilder responseStrBuilder = new StringBuilder();
String inputStr;
while ((inputStr = reader.readLine()) != null) {
responseStrBuilder.append(inputStr);
}
// Close the connection
writer.close();
reader.close();
LOG.debug(String.format("Finished swapping OAuth token for a JWT"));
return responseStrBuilder.toString();
}
}
