(Excel) Verify a JWT Created by the Amazon Cognito Service

Demonstrates how to verify a JWT created by the Amazon Cognito Service.

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

' The public keys for this example are at https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json
' Let's get them:

Dim http As Chilkat.Http
Set http = Chilkat.NewHttp
Dim sbJsonKeys As Chilkat.StringBuilder
Set sbJsonKeys = Chilkat.NewStringBuilder

success = http.QuickGetSb("https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json",sbJsonKeys)
If (success = False) Then
    Debug.Print http.LastErrorText
    Exit Sub
End If

Dim jsonKeys As Chilkat.JsonObject
Set jsonKeys = Chilkat.NewJsonObject
Dim success As Boolean
success = jsonKeys.LoadSb(sbJsonKeys)
jsonKeys.EmitCompact = False
Debug.Print jsonKeys.Emit()

' Here are the keys:

' {
'   "keys": [
'     {
'       "alg": "RS256",
'       "e": "AQAB",
'       "kid": "1A/L5Fsb2EsEwxy5E0cmCMS1BnMe6Jl6NXiMig4iNwU=",
'       "kty": "RSA",
'       "n": "y0w7BJrIJYi ... jKG27z2P3OKw",
'       "use": "sig"
'     },
'     {
'       "alg": "RS256",
'       "e": "AQAB",
'       "kid": "mos6VTJnvDwurY3ghJg6IAPUq+dMwl6CL/iThzJOkzg=",
'       "kty": "RSA",
'       "n": "qbIEH-7tg6yrT ... 3Fj94ooTd0w",
'       "use": "sig"
'     }
'   ]
' }

' Try the 1st key.

Set jsonKey1 = jsonKeys.ObjectOf("keys[0]")
If (jsonKeys.LastMethodSuccess = False) Then
    Debug.Print "Did not get the 1st JSON public key."
    Exit Sub
End If

Dim pubKey1 As Chilkat.PublicKey
Set pubKey1 = Chilkat.NewPublicKey
success = pubKey1.LoadFromString(jsonKey1.Emit())
If (success = False) Then
    Debug.Print pubKey1.LastErrorText
    Exit Sub
End If

Debug.Print "Success"

Dim jwt As Chilkat.Jwt
Set jwt = Chilkat.NewJwt

' I did not include the an actual AWS Cognito token here because our test sample used customer-provided data..

token = "eyJ..asXg"

' First verify the signature.

sigVerified = jwt.VerifyJwtPk(token,pubKey1)
Debug.Print "verified: "; sigVerified

' Let's see if the time constraints, if any, are valid.
' The above JWT was created on the afternoon of 16-May-2016, with an expiration of 1 hour.
' If the current system time is before the "nbf" time, or after the "exp" time,
' then IsTimeValid will return false/0.
' Also, we'll allow a leeway of 60 seconds to account for any clock skew.
' Note: If the token has no "nbf" or "exp" claim fields, then IsTimeValid is always true.

leeway = 60

bTimeValid = jwt.IsTimeValid(token,leeway)
Debug.Print "time constraints valid: "; bTimeValid

' Now let's recover the original claims JSON (the payload).

payload = jwt.GetPayload(token)
' The payload will likely be in compact form:
Debug.Print payload

' We can format for human viewing by loading it into Chilkat's JSON object
' and emit.
Dim json As Chilkat.JsonObject
Set json = Chilkat.NewJsonObject
success = json.Load(payload)
json.EmitCompact = False
Debug.Print json.Emit()

' We can recover the original JOSE header in the same way:

joseHeader = jwt.GetHeader(token)
' The payload will likely be in compact form:
Debug.Print joseHeader

' We can format for human viewing by loading it into Chilkat's JSON object
' and emit.
success = json.Load(joseHeader)
json.EmitCompact = False
Debug.Print json.Emit()