How to verify firebase ID token with PHP(JWT)?

Question

I have a shared hosting plan which has only PHP(no Java, no node.js). I need to send firebase ID token from my android app and verify it by PHP-JWT.

I am following t

Answer 1

Instead of doing it all manually, you can take a look at this library:
Firebase Tokens or even Firebase Admin SDK for PHP. Caching stuff etc. is already implemented, just take a look at the docs.

Basically you would simply do the following using Firebase Tokens Library:

use Firebase\Auth\Token\HttpKeyStore;
use Firebase\Auth\Token\Verifier;
use Symfony\Component\Cache\Simple\FilesystemCache;

$cache = new FilesystemCache();
$keyStore = new HttpKeyStore(null, $cache);
$verifier = new Verifier($projectId, $keyStore);

    try {
        $verifiedIdToken = $verifier->verifyIdToken($idToken);

        // "If all the above verifications are successful, you can use the subject 
        // (sub) of the ID token as the uid of the corresponding user or device. (see https://firebase.google.com/docs/auth/admin/verify-id-tokens#verify_id_tokens_using_a_third-party_jwt_library)
        echo $verifiedIdToken->getClaim('sub'); // "a-uid"
    } catch (\Firebase\Auth\Token\Exception\ExpiredToken $e) {
        echo $e->getMessage();
    } catch (\Firebase\Auth\Token\Exception\IssuedInTheFuture $e) {
        echo $e->getMessage();
    } catch (\Firebase\Auth\Token\Exception\InvalidToken $e) {
        echo $e->getMessage();
    }