PHP JWT Token Invalid Signature

Question

I'm searching for an hours now and can't find a solution to this problem.

This is the code to generate JWT token. I used https://github.com/firebase/php-jwt library.

        $tokenId    = base64_encode(mcrypt_create_iv(32));
        $issuedAt   = time();
        $notBefore  = $issuedAt + 10;             //Adding 10 seconds
        $expire     = $notBefore + 60;            // Adding 60 seconds
        $serverName = 'serverName'; // Retrieve the server name from config file

        $secretKey = base64_decode(getenv('JWT_SECRET'));

         $data = [
            'iat'  => $issuedAt,         // Issued at: time when the token was generated
            'jti'  => $tokenId,          // Json Token Id: an unique identifier for the token
            'iss'  => $serverName,       // Issuer
            'nbf'  => $notBefore,        // Not before
            'exp'  => $expire,           // Expire
            'data' => [                  // Data related to the signer user
                'userId'   => '1', // userid from the users table
                'userName' => $UserName, // User name
            ]
        ];

        $jwt = JWT::encode(
                $data,      //Data to be encoded in the JWT
                $secretKey, // The signing key
                'HS256'     // Algorithm used to sign the token
        );

        $unencodedArray = ['jwt' => $jwt];
        echo json_encode($unencodedArray);

And I verify the token at https://jwt.io/

Can anybody help me with this problem? I'm currently new in JWT. Btw, my project is Slim API.

Thank you very much.

Answer 1

Signature verification fails because you are not passing the correct secret key to https://jwt.io/ You need to pass the value of $secretKey from the PHP code. According to the screenshot you are passing string secret.