email_verified = false in ID token from Google - jwt

Question

I use Google ID tokens to sign in users to my webservice. As part of validating the token it receives from Google, the webservice checks that email_verified = true in the token's payload.
Some of my users signed up for a Google-account with their non-Gmail, non-Google Apps email address. They did click the link in the email that Google sent them after sign-up, to verify their email address.
When those users try to login to my webservice, I get email_verified = false in the token's payload.
What does this mean and can/ should I ignore this in validating the token?

Answer 1

There are a couple of different ways in which you can validate the integrity of the ID token on the server side:
"Manually" - constantly download Google's public keys, verify signature and then each and every field, including the iss one; the main advantage (albeit a small one in my opinion) I see here is that you can minimize the number of requests sent to Google.
"Automatically" - do a GET on Google's endpoint to verify this token
https://www.googleapis.com/oauth2/v3/tokeninfo?id_token={0}
Using a Google API Client Library - like the official one.
Here's how this could look:
private const string GoogleApiTokenInfoUrl = "https://www.googleapis.com/oauth2/v3/tokeninfo?id_token={0}";
public ProviderUserDetails GetUserDetails(string providerToken)
{
var httpClient = new MonitoredHttpClient();
var requestUri = new Uri(string.Format(GoogleApiTokenInfoUrl, providerToken));
HttpResponseMessage httpResponseMessage;
try
{
httpResponseMessage = httpClient.GetAsync(requestUri).Result;
}
catch (Exception ex)
{
return null;
}
if (httpResponseMessage.StatusCode != HttpStatusCode.OK)
{
return null;
}
var response = httpResponseMessage.Content.ReadAsStringAsync().Result;
var googleApiTokenInfo = JsonConvert.DeserializeObject<GoogleApiTokenInfo>(response);
if (!SupportedClientsIds.Contains(googleApiTokenInfo.aud))
{
Log.WarnFormat("Google API Token Info aud field ({0}) not containing the required client id", googleApiTokenInfo.aud);
return null;
}
return new ProviderUserDetails
{
Email = googleApiTokenInfo.email,
FirstName = googleApiTokenInfo.given_name,
LastName = googleApiTokenInfo.family_name,
Locale = googleApiTokenInfo.locale,
Name = googleApiTokenInfo.name,
ProviderUserId = googleApiTokenInfo.sub
};
}