(.NET Core C#) Verify a Google JWT Using Google's Public Key

See more Google APIs Examples

Demonstrates how to verify a JWT that was signed using Google's RSA private key.

This example verifies the RSA signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

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// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

Chilkat.Http http = new Chilkat.Http();
Chilkat.StringBuilder sbPubKeys = new Chilkat.StringBuilder();

bool success = http.QuickGetSb("https://www.googleapis.com/oauth2/v3/certs",sbPubKeys);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

Debug.WriteLine(sbPubKeys.GetAsString());

// Here are the keys:

// {
//   "keys": [
//     {
//       "e": "AQAB",
//       "n": "4bAT6C6EeX8Dspje3FrAXw-nnhNk04e1RmNa4kjc0CHf6Pk7ryARlwA-6YilyPABqQfYHx60s8oSnxvUVprFfQ2-Q8aAZO7bPKSxnoGlcKERL2oLNA4Msvc89N9Y5ycThZUplf_QC19e6jyYXN6Nz-UnJSCLrtQY8tVhhVRs61j4A2N_p-enAi-r704Qi1-v-DKV4eVRkClKViploo8NyjUaT9L4vbBssPCjyimJzsWnEe1fED5c4LnHeArYzA_FEn3JJotqDIz9t2VnvZNTMhizHEX4VnORlEWMEfR8n4CEHQx7PcQUOmfqyw08gWeXQl1-uTjtIGaE-sRIv9u_vQ",
//       "kty": "RSA",
//       "use": "sig",
//       "alg": "RS256",
//       "kid": "2af90e87be140c20038898a6efa11283dab6031d"
//     },
//     {
//       "n": "nzGsrziOYrMVYMpvUZOwkKNiPWcOPTYRYlDSdRW4UpAHdWPbPlyqaaphYhoMB5DXrVxI3bdvm7DOlo-sHNnulmAFQa-7TsQMxrZCvVdAbyXGID9DZYEqf8mkCV1Ohv7WY5lDUqlybIk1OSHdK7-1et0QS8nn-5LojGg8FK4ssLf3mV1APpujl27D1bDhyRb1MGumXYElwlUms7F9p9OcSp5pTevXCLmXs9MJJk4o9E1zzPpQ9Ko0lH9l_UqFpA7vwQhnw0nbh73rXOX2TUDCUqL4ThKU5Z9Pd-eZCEOatKe0mJTpQ00XGACBME_6ojCdfNIJr84Y_IpGKvkAEksn9w",
//       "use": "sig",
//       "kid": "87bbe0815b064e6d449cac999f0e50e72a3e4374",
//       "e": "AQAB",
//       "alg": "RS256",
//       "kty": "RSA"
//     }
//   ]
// }

// -------------------------------------------------------------------------------------------
// Replace this with your actual token.
// This sample token contains a kid that does not match any of the above Google public keys.
// -------------------------------------------------------------------------------------------
string token = "eyJhbGciOiJSUzI1NiIsImtpZCI6IjQyZmY5MGQ3ZDM0OGM5NzM4MWE3YzExOWVmMWY1MzI0ZWEzZjViZWIifQ.eyJpc3MiOiJodHRwczovL2FjY291bnRzLmdvb2dsZS5jb20iLCJzdWIiOiIxMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExIiwiaWF0IjoxNjExMTE1MTQzLCJleHAiOjE2MTEyMDE1NDMsImF1ZCI6IjQyOTc1NzExNTE0ODg0OSJ9.pLem5i0bx3M7lJYj7jKv2Nq7c07X5YpZz-x1uM5RniW-v4LsX-lKIVvOq2x3-WoPqkzLXJfP0kG0dx1uD2q1NfFQK60YwKH4FnFtB6INnUP1dRVpP9_pTTKyAE28I3s5Tay4PbPdrCl7ZLCIJzCfpCW1TiWeVoPjp5HgZKTBHdP_sEkN_yO5dQerQXAkFJkV3kNgF9jI3ayT-KPqOIH6GVoWXjHFDyA2EYgJPEFRo5WSe6XycJ85p5duwT-OoBcb_kJZG9PxYd91eHlPCzp8vGxzIb2dVROCBxyM8e8W0cd9v15hfmpg9R-eG9vCM5y63ZLChZLFeHFx0Pd7hvAqfKg";

Chilkat.Jwt jwt = new Chilkat.Jwt();
string header = jwt.GetHeader(token);

Debug.WriteLine(header);

// Sample header:
// {"alg":"RS256","kid":"87bbe0815b064e6d449cac999f0e50e72a3e4374"}

// Load the public key matching the "kid" into a Chilkat public key object, then verify..

Chilkat.JsonObject json = new Chilkat.JsonObject();
json.Load(header);
string kid = json.StringOf("kid");

Debug.WriteLine("kid = " + kid);

Chilkat.JsonObject jsonPubKeys = new Chilkat.JsonObject();
jsonPubKeys.LoadSb(sbPubKeys);

Chilkat.JsonObject jsonKey = jsonPubKeys.FindRecord("keys","kid",kid,true);
if (jsonPubKeys.LastMethodSuccess == false) {
    Debug.WriteLine("Did not find a matching public key based on the kid.");
    return;
}

Debug.WriteLine(jsonKey.Emit());

// Load the matching public key into a Chilkat public key object.
Chilkat.PublicKey pubKey = new Chilkat.PublicKey();
success = pubKey.LoadFromString(jsonKey.Emit());

if (success == false) {
    Debug.WriteLine(pubKey.LastErrorText);
    return;
}

// ----------------------------------------------------------------------------------------
// Now we can validate the JWT using Google's public key as shown in this example:
// (Except we use the public key obtained as shown above instead of a public key loaded from a PEM file.
// 
// See Verify JWT Using an RSA Public Key