(MFC) Validate a Google ID Token

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

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkHttp.h>
#include <CkJsonObject.h>
#include <CkStringBuilder.h>
#include <CkRsa.h>
#include <CkPublicKey.h>

void ChilkatSample(void)
    {
    CkString strOut;

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

    CkHttp http;

    // First get the public key we'll be needing..
    const char *jwkStr = http.quickGetStr("https://www.googleapis.com/oauth2/v3/certs");
    if (http.get_LastMethodSuccess() == false) {
        strOut.append(http.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // 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"
    // 	}
    //       ]
    //     }

    CkJsonObject json;
    bool 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"
    // }

    CkJsonObject jsonToken;
    success = jsonToken.LoadFile("qa_data/tokens/google_sample_id_token.json");
    if (success == false) {
        strOut.append("Failed to load the JSON file...");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // Get the id_token;
    CkStringBuilder sbIdToken;
    success = sbIdToken.Append(jsonToken.stringOf("id_token"));

    // Get the signature in base64url format.
    // The header + payload remains in sbIdToken.
    const char *sig_b64Url = sbIdToken.getAfterFinal(".",true);
    const char *headerPlusPayload = sbIdToken.getAsString();

    strOut.append(sig_b64Url);
    strOut.append("\r\n");
    strOut.append(headerPlusPayload);
    strOut.append("\r\n");

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

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

    CkRsa rsa;
    rsa.put_EncodingMode("base64url");

    int numKeys = json.SizeOfArray("keys");
    int i = 0;
    while (i < numKeys) {
        json.put_I(i);
        CkJsonObject *jsonKey = json.ObjectOf("keys[i]");
        CkPublicKey pubKey;
        success = pubKey.LoadFromString(jsonKey->emit());
        if (success == false) {
            strOut.append(pubKey.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        strOut.appendInt(i);
        strOut.append("\r\n");
        strOut.append(pubKey.getPem(true));
        strOut.append("\r\n");
        delete jsonKey;

        success = rsa.ImportPublicKeyObj(pubKey);

        bool bVerified = rsa.VerifyStringENC(headerPlusPayload,"sha256",sig_b64Url);
        strOut.append("bVerified = ");
        strOut.appendInt(bVerified);
        strOut.append("\r\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


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }