(Excel) 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 Chilkat.JsonObject
Set jsonToken = Chilkat.NewJsonObject

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 Chilkat.JsonObject
Set jsonWebKeys = Chilkat.NewJsonObject
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 Chilkat.Jwt
Set jwt = Chilkat.NewJwt

accessToken = jsonToken.StringOf("access_token")

joseHeader = jwt.GetHeader(accessToken)

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

Dim json As Chilkat.JsonObject
Set json = Chilkat.NewJsonObject
success = json.Load(joseHeader)

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 Chilkat.StringBuilder
Set sbKid = Chilkat.NewStringBuilder

e = ""

n = ""


i = 0

count_i = jsonWebKeys.SizeOfArray("keys")

bFound = False

iMatch = 0
Do While (bFound = False) 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,True) = True) Then
        e = jsonWebKeys.StringOf("keys[i].e")
        n = jsonWebKeys.StringOf("keys[i].n")
        ' Exit the loop. 
        Debug.Print "Found matching kid."
        iMatch = i
        bFound = True
    End If

    i = i + 1
Loop

If (bFound = False) 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 Chilkat.PublicKey
Set pubkey = Chilkat.NewPublicKey

' Get the matching JSON key from the array of keys.
jsonWebKeys.I = iMatch

Set jsonWebKey = jsonWebKeys.ObjectOf("keys[i]")
success = pubkey.LoadFromString(jsonWebKey.Emit())
If (success = False) 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.

bVerified = jwt.VerifyJwtPk(accessToken,pubkey)
If (bVerified = True) Then
    Debug.Print "The access token is valid."
Else
    Debug.Print "The access token is NOT valid."
End If