Invalid JWT when trying to connect to Google Oauth for google API

Question

I was trying to connect to Google API through OAuth through JWT, but I keep getting this error:

{ "error": "invalid_grant", "error_description": "Invalid JWT: Token must be a short-lived token and in a reasonable timeframe" }

In my JWT calim I set the iat to be current time minus 1970-01-01 in seconds and exp to iat + 3600, so I do not know why I am still getting this error. If anyone knows the answer please tell meeeeee!

Solution 1

Not sure if you ever got it to work, but the following simple steps worked for me using the PHP function openssl_sign():

//helper function
function base64url_encode($data) { 
    return rtrim(strtr(base64_encode($data), '+/', '-_'), '='); 
}

//Google's Documentation of Creating a JWT: https://developers.google.com/identity/protocols/OAuth2ServiceAccount#authorizingrequests

//{Base64url encoded JSON header}
$jwtHeader = base64url_encode(json_encode(array(
    "alg" => "RS256",
    "typ" => "JWT"
)));
//{Base64url encoded JSON claim set}
$now = time();
$jwtClaim = base64url_encode(json_encode(array(
    "iss" => "[e-mail]",
    "scope" => "https://www.googleapis.com/auth/prediction",
    "aud" => "https://www.googleapis.com/oauth2/v4/token",
    "exp" => $now + 3600,
    "iat" => $now
)));
//The base string for the signature: {Base64url encoded JSON header}.{Base64url encoded JSON claim set}
openssl_sign(
    $jwtHeader.".".$jwtClaim,
    $jwtSig,
    $your_private_key_from_google_api_console,
    "sha256WithRSAEncryption"
);
$jwtSign = base64url_encode($jwtSig);

//{Base64url encoded JSON header}.{Base64url encoded JSON claim set}.{Base64url encoded signature}
$jwtAssertion = $jwtHeader.".".$jwtClaim.".".$jwtSig;

Solution 2

I had the same issue, I solved it by syncing my VMs time to have the correct one with a public ntpserver:

ntpdate ntp.ubuntu.com

Solution 3

You have to set a correct expiration time for the token if you see this error. Example:

var currentTime = new Date().getTime() / 1000; //must be in seconds
var exp = currentTime + 60;

var auth_claimset = {
      iss       :   "...",
      scope     :   "...",
      aud       :   "...",
      exp       :   exp,
      iat       :   currentTime 
};

Comments

[andy]

So I have modified to the below code: ' $sig = hash('SHA256', $headerAndPayload, $secret); $signature = base64url_encode($sig); $jwt = $headerAndPayload . "." . $signature; ' I keep getting a signature invalid for some reason. $secret is the private key i obtained from service account key json file. Would you know what's wrong?

[andy]

I just found out that using hash in PHP does not use a secret key, so I should probably still use hash_hmac, and I am not getting a result :/

[user2705223]

There appear to be signing libraries that create spec compliant JWTs. For example: github.com/namshi/jose

[andy]

Sorry I kept forgetting to update this. This was indeed the right answer! Although I don't need to use this anymore because App Engine allows me to directly reach Cloud Storage now. But still thank you for the right answer! :)

[Michel]

Hey @Joseph Shih I am having similar issue, my error is Invalid JWT Signature.. Can you share your POST request. I guess I'm having issues with grant_type in the request body.

[Joseph Shih]

@Michel, an invalid JWT signature error means that your signature failed to authenticate your $jwtHeader and $jwtClaim. Are you using the correct ISS (email address of the service account) and are you using the private key from your API console. Also, remember you'll need to base-64 encode the signature (like the example above).

[Michel]

Never mind @JosephShih I was able to fix it. I posted the answer here: stackoverflow.com/questions/48106432/… Still thanks for the reply :)