B4X Requires Chilkat v11.0.0+
Verify a JWT Created by the Amazon Cognito Service

Demonstrates how to verify a JWT created by the Amazon Cognito Service.
Chilkat B4X Downloads

B4X
Dim success As Boolean = False

'  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 ChilkatHttp
http.Initialize("http")
Dim sbJsonKeys As ChilkatStringBuilder
sbJsonKeys.Initialize
success = http.QuickGetSb("https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json", sbJsonKeys)
If success = False Then
    Log(http.LastErrorText)
    Return
End If


Dim jsonKeys As ChilkatJsonObject
jsonKeys.Initialize
jsonKeys.LoadSb(sbJsonKeys)
jsonKeys.EmitCompact = False
Log(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.
Dim jsonKey1 As ChilkatJsonObject
jsonKey1.Initialize
jsonKeys.ObjectOf2("keys[0]", jsonKey1)

Dim pubKey1 As ChilkatPublicKey
pubKey1.Initialize
success = pubKey1.LoadFromString(jsonKey1.Emit)
If success = False Then
    Log(pubKey1.LastErrorText)
    Return
End If


Log("Success")

Dim jwt As ChilkatJwt
jwt.Initialize

'  I did not include the an actual AWS Cognito token here because our test sample used customer-provided data..
Dim token As String = "eyJ..asXg"

'  First verify the signature.
Dim sigVerified As Boolean = jwt.VerifyJwtPk(token, pubKey1)
Log("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.
Dim leeway As Int = 60
Dim bTimeValid As Boolean = jwt.IsTimeValid(token, leeway)
Log("time constraints valid: " & bTimeValid)

'  Now let's recover the original claims JSON (the payload).
Dim payload As String = jwt.GetPayload(token)
'  The payload will likely be in compact form:
Log(payload)

'  We can format for human viewing by loading it into Chilkat's JSON object
'  and emit.
Dim json As ChilkatJsonObject
json.Initialize
success = json.Load(payload)
json.EmitCompact = False
Log(json.Emit)

'  We can recover the original JOSE header in the same way:
Dim joseHeader As String = jwt.GetHeader(token)
'  The payload will likely be in compact form:
Log(joseHeader)

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