(Xojo Plugin) Validate a Google ID Token

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

Chilkat Xojo Plugin Download Xojo Plugin for Windows, Linux, Mac OS X, and ARM, ARM64

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

Dim http As New Chilkat.Http

// First get the public key we'll be needing..
Dim jwkStr As String
jwkStr = http.QuickGetStr("https://www.googleapis.com/oauth2/v3/certs")
If (http.LastMethodSuccess = False) Then
    System.DebugLog(http.LastErrorText)
    Return
End If

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

Dim json As New Chilkat.JsonObject
Dim success As Boolean
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"
// }

Dim jsonToken As New Chilkat.JsonObject
success = jsonToken.LoadFile("qa_data/tokens/google_sample_id_token.json")
If (success = False) Then
    System.DebugLog("Failed to load the JSON file...")
    Return
End If

// Get the id_token;
Dim sbIdToken As New Chilkat.StringBuilder
success = sbIdToken.Append(jsonToken.StringOf("id_token"))

// Get the signature in base64url format.
// The header + payload remains in sbIdToken.
Dim sig_b64Url As String
sig_b64Url = sbIdToken.GetAfterFinal(".",True)
Dim headerPlusPayload As String
headerPlusPayload = sbIdToken.GetAsString()

System.DebugLog(sig_b64Url)
System.DebugLog(headerPlusPayload)

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

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

Dim rsa As New Chilkat.Rsa
rsa.EncodingMode = "base64url"

Dim numKeys As Int32
numKeys = json.SizeOfArray("keys")
Dim i As Int32
i = 0
While i < numKeys
    json.I = i
    Dim jsonKey As Chilkat.JsonObject
    jsonKey = json.ObjectOf("keys[i]")
    Dim pubKey As New Chilkat.PublicKey
    success = pubKey.LoadFromString(jsonKey.Emit())
    If (success = False) Then
        System.DebugLog(pubKey.LastErrorText)
        Return
    End If

    System.DebugLog(Str(i))
    System.DebugLog(pubKey.GetPem(True))

    success = rsa.ImportPublicKeyObj(pubKey)

    Dim bVerified As Boolean
    bVerified = rsa.VerifyStringENC(headerPlusPayload,"sha256",sig_b64Url)
    System.DebugLog("bVerified = " + Str(bVerified))

    i = i + 1
Wend

// 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