(PHP Extension) Validate a Google ID Token

Demonstrates how to verify the signature of a Google id token.

Chilkat PHP Downloads PHP Extension for Windows, Linux, MacOS, Alpine Linux, Solaris

<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

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

$http = new CkHttp();

// First get the public key we'll be needing..
$jwkStr = $http->quickGetStr('https://www.googleapis.com/oauth2/v3/certs');
if ($http->get_LastMethodSuccess() == false) {
    print $http->lastErrorText() . "\n";
    exit;
}

// We have the following:

//     {
//       "keys": [
// 	{
// 	  "kid": "e8732db06287515556213b80acbcfd08cfb302a9",
// 	  "n": "4RIrO30287Wsq3gqXCMkUYMVAeI3H8...w2mbMNEBQ",
// 	  "kty": "RSA",
// 	  "e": "AQAB",
// 	  "alg": "RS256",
// 	  "use": "sig"
// 	},
// 	{
// 	  "kid": "8462a71da4f6d611fc0fecf0fc4ba9c37d65e6cd",
// 	  "e": "AQAB",
// 	  "n": "xT_ngLZNmT5GBtJZeTB...Ft4gK0eoFi0d3l8bcw",
// 	  "alg": "RS256",
// 	  "use": "sig",
// 	  "kty": "RSA"
// 	}
//       ]
//     }

$json = new CkJsonObject();
$success = $json->Load($jwkStr);

// -------------------------------------------------

// Load the following..

//  {
//   "access_token": "ya29.a0...0f",
//   "expires_in": 3599,
//   "scope": "openid https://www.googleapis.com/auth/userinfo.email",
//   "token_type": "Bearer",
//   "id_token": "eyJhb...o5nQ"
// }

$jsonToken = new CkJsonObject();
$success = $jsonToken->LoadFile('qa_data/tokens/google_sample_id_token.json');
if ($success == false) {
    print 'Failed to load the JSON file...' . "\n";
    exit;
}

// Get the id_token;
$sbIdToken = new CkStringBuilder();
$success = $sbIdToken->Append($jsonToken->stringOf('id_token'));

// Get the signature in base64url format.
// The header + payload remains in sbIdToken.
$sig_b64Url = $sbIdToken->getAfterFinal('.',true);
$headerPlusPayload = $sbIdToken->getAsString();

print $sig_b64Url . "\n";
print $headerPlusPayload . "\n";

// ---------------------------------------------

// Try validating with each cert's public key.
// Hopefully one will be the key that verifies.

$rsa = new CkRsa();
$rsa->put_EncodingMode('base64url');

$numKeys = $json->SizeOfArray('keys');
$i = 0;
while ($i < $numKeys) {
    $json->put_I($i);
    // jsonKey is a CkJsonObject
    $jsonKey = $json->ObjectOf('keys[i]');
    $pubKey = new CkPublicKey();
    $success = $pubKey->LoadFromString($jsonKey->emit());
    if ($success == false) {
        print $pubKey->lastErrorText() . "\n";
        exit;
    }

    print $i . "\n";
    print $pubKey->getPem(true) . "\n";

    $success = $rsa->ImportPublicKeyObj($pubKey);

    $bVerified = $rsa->VerifyStringENC($headerPlusPayload,'sha256',$sig_b64Url);
    print 'bVerified = ' . $bVerified . "\n";

    $i = $i + 1;
}

// The output is:

// 0
// -----BEGIN RSA PUBLIC KEY-----
// MIIBCgKCAQEA4RIrO30287Wsq3gqXCMkUYMVAeI3H8LVE6IXR1krdFeGnZLiGUPw
// cbkeVpXf3lmJdsStOg+jijces2DZCfPyIBiQuLYfxxmAZE6ErJ0QJFg1stwli2Pz
// 9ncYhFoqi8pXr7kEzEJBTzX4thuw56ydbGsshSEznPXoerCJOc7UI2+n0wFCWQ4Y
// LHbh/PrWt4vdadyUUUW/QpQHXQLdD8q/Qwqdj0O9zlJE7R6Elw2E9EqnHyIGu1hm
// LxhqrTru1M18SUhONYbVskV/BCEdVKs//X96849HorWQDCAgVMWfGsdMVq55FAdJ
// 680N5UmQDRynIZ4+PeNGN4S9iw2mbMNEBQIDAQAB
// -----END RSA PUBLIC KEY-----
// 
// bVerified = True
// 1
// -----BEGIN RSA PUBLIC KEY-----
// MIIBCgKCAQEAxT/ngLZNmT5GBdkLtJZjNeTB+8B5yWgrq/e5eMZ1hrZhcmLK+dSn
// IkpOPV8/OekV67EnQ7I4II2rcNJnHGrGKZziXO3XN2gtUHE+mBJC99oULSbX/QwB
// Kz7gC/IBPq9EuxTt6Oq6fPkVQ9DbRIgWJSEGBF/KRaNl3kyAlIZfpY7XgHyJTTv8
// E7yAcYKPR+36gzdl+ps0sDLKzUuAtZNq8llK0u80z6AtAUIYwWdkEhM9upy6keKI
// TasIxcsO7M6kZPINUSbh6t5VAm8FuqRmxpgg+9c9/GQSGd89InVypoVzWLQ+wOGg
// 5G4H6JqIgtj0TRFt4gK0eoFi2U0d3l8bcwIDAQAB
// -----END RSA PUBLIC KEY-----
// 
// bVerified = False

?>