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

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

Chilkat .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# 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:

$http = New-Object Chilkat.Http
$sbJsonKeys = New-Object Chilkat.StringBuilder
$success = $http.QuickGetSb("https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json",$sbJsonKeys)
if ($success -eq $false) {
    $($http.LastErrorText)
    exit
}

$jsonKeys = New-Object Chilkat.JsonObject
$jsonKeys.LoadSb($sbJsonKeys)
$jsonKeys.EmitCompact = $false
$($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.
$jsonKey1 = $jsonKeys.ObjectOf("keys[0]")
if ($jsonKeys.LastMethodSuccess -eq $false) {
    $("Did not get the 1st JSON public key.")
    exit
}

$pubKey1 = New-Object Chilkat.PublicKey
$success = $pubKey1.LoadFromString($jsonKey1.Emit())
if ($success -eq $false) {
    $($pubKey1.LastErrorText)
    exit
}

$("Success")

$jwt = New-Object Chilkat.Jwt

# 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)
$("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)
$("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:
$($payload)

# We can format for human viewing by loading it into Chilkat's JSON object
# and emit.
$json = New-Object Chilkat.JsonObject
$success = $json.Load($payload)
$json.EmitCompact = $false
$($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:
$($joseHeader)

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