(Visual Basic 6.0) Verify Okta Access Token Locally

This example demonstrates how to validate an Okta access token using Chilkat's JWT class.

For more information, see https://developer.okta.com/docs/guides/validate-access-tokens/overview/#what-to-check-when-validating-an-access-token

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

' This example begins with two JSON files:
' 
' 1. The access token obtained from Okta as shown in one fo these examples:  
'    Get Okta Token using Resource Owner Password Flow
' 
' 2. The Okta web keys obtained by this example:  Get Okta Web Keys
' 
' 

' Load the access token to be verified.
' It contains JSON that looks like this:
' {
'   "access_token": "eyJraWQiOiJhb ... O_eVu-kBp6g",
'   "token_type": "Bearer",
'   "expires_in": 3600,
'   "scope": "openid",
'   "id_token": "eyJraWQi ... FrL9WOuwbQtUg"
' }
' This example verifies the access_token.  (The id_token is verified in this example:  Verify Okta ID Token

Dim jsonToken As New ChilkatJsonObject
Dim success As Long
success = jsonToken.LoadFile("qa_data/tokens/okta_access_token.json")

' Load the public keys (Okta web keys), one of which is needed to validate.
' The web keys JSON looks like this:
' {
'   "keys": [
'     {
'       "kty": "RSA",
'       "alg": "RS256",
'       "kid": "anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ",
'       "use": "sig",
'       "e": "AQAB",
'       "n": "jT8uAgd5w ... euLB1HaVw"
'     },
'     {
' 	...
'     }
'   ]
' }

Dim jsonWebKeys As New ChilkatJsonObject
success = jsonWebKeys.LoadFile("qa_data/tokens/okta_web_keys.json")

' ------------------------
' Step 1: Get the JOSE header from the JWT.  The JOSE header contains JSON.  One of the JSON members will be the key ID "kid" which identifies the web key to be used for validation.
' 
Dim jwt As New ChilkatJwt
Dim accessToken As String
accessToken = jsonToken.StringOf("access_token")
Dim joseHeader As String
joseHeader = jwt.GetHeader(accessToken)

Debug.Print joseHeader
' The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

Dim json As New ChilkatJsonObject
success = json.Load(joseHeader)
Dim kid As String
kid = json.StringOf("kid")
Debug.Print "kid to find: " & kid

' ------------------------
' Step 2: Find the key with the same "kid" in the Okta web keys.

Dim sbKid As New ChilkatStringBuilder
Dim e As String
e = ""
Dim n As String
n = ""

Dim i As Long
i = 0
Dim count_i As Long
count_i = jsonWebKeys.SizeOfArray("keys")
Dim bFound As Long
bFound = 0
Dim iMatch As Long
iMatch = 0
Do While (bFound = 0) And (i < count_i)
    jsonWebKeys.I = i
    sbKid.Clear 
    success = jsonWebKeys.StringOfSb("keys[i].kid",sbKid)
    Debug.Print "checking kid: " & sbKid.GetAsString()

    If (sbKid.ContentsEqual(kid,1) = 1) Then
        e = jsonWebKeys.StringOf("keys[i].e")
        n = jsonWebKeys.StringOf("keys[i].n")
        ' Exit the loop. 
        Debug.Print "Found matching kid."
        iMatch = i
        bFound = 1
    End If

    i = i + 1
Loop

If (bFound = 0) Then
    Debug.Print "No matching key ID found."
    Exit Sub
End If

Debug.Print "Matching key:"
Debug.Print "  exponent = " & e
Debug.Print "  modulus = " & n

' ------------------------
' Step 3: Load the RSA modulus and exponent into a Chilkat public key object.
Dim pubkey As New PublicKey

' Get the matching JSON key from the array of keys.
jsonWebKeys.I = iMatch
Dim jsonWebKey As ChilkatJsonObject
Set jsonWebKey = jsonWebKeys.ObjectOf("keys[i]")
success = pubkey.LoadFromString(jsonWebKey.Emit())
If (success = 0) Then
    Debug.Print "Failed to load JSON web key."
    Debug.Print jsonWebKey.Emit()
    Debug.Print pubkey.LastErrorText

    Exit Sub
End If

Debug.Print "successfully loaded web key."

' OK.. we have the desired JSON web key loaded into our public key object.
' Now we can verify the access token.

' ------------------------
' Step 4: Verify the access token.
Dim bVerified As Long
bVerified = jwt.VerifyJwtPk(accessToken,pubkey)
If (bVerified = 1) Then
    Debug.Print "The access token is valid."
Else
    Debug.Print "The access token is NOT valid."
End If