(PowerShell) Verify a Google JWT Using Google's Public Key

See more Google APIs Examples

Demonstrates how to verify a JWT that was signed using Google's RSA private key.

This example verifies the RSA signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

Chilkat .NET Downloads Chilkat .NET Assemblies

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

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

$http = New-Object Chilkat.Http
$sbPubKeys = New-Object Chilkat.StringBuilder

$success = $http.QuickGetSb("https://www.googleapis.com/oauth2/v3/certs",$sbPubKeys)
if ($success -eq $false) {
    $($http.LastErrorText)
    exit
}

$($sbPubKeys.GetAsString())

# Here are the keys:

# {
#   "keys": [
#     {
#       "e": "AQAB",
#       "n": "4bAT6C6EeX8Dspje3FrAXw-nnhNk04e1RmNa4kjc0CHf6Pk7ryARlwA-6YilyPABqQfYHx60s8oSnxvUVprFfQ2-Q8aAZO7bPKSxnoGlcKERL2oLNA4Msvc89N9Y5ycThZUplf_QC19e6jyYXN6Nz-UnJSCLrtQY8tVhhVRs61j4A2N_p-enAi-r704Qi1-v-DKV4eVRkClKViploo8NyjUaT9L4vbBssPCjyimJzsWnEe1fED5c4LnHeArYzA_FEn3JJotqDIz9t2VnvZNTMhizHEX4VnORlEWMEfR8n4CEHQx7PcQUOmfqyw08gWeXQl1-uTjtIGaE-sRIv9u_vQ",
#       "kty": "RSA",
#       "use": "sig",
#       "alg": "RS256",
#       "kid": "2af90e87be140c20038898a6efa11283dab6031d"
#     },
#     {
#       "n": "nzGsrziOYrMVYMpvUZOwkKNiPWcOPTYRYlDSdRW4UpAHdWPbPlyqaaphYhoMB5DXrVxI3bdvm7DOlo-sHNnulmAFQa-7TsQMxrZCvVdAbyXGID9DZYEqf8mkCV1Ohv7WY5lDUqlybIk1OSHdK7-1et0QS8nn-5LojGg8FK4ssLf3mV1APpujl27D1bDhyRb1MGumXYElwlUms7F9p9OcSp5pTevXCLmXs9MJJk4o9E1zzPpQ9Ko0lH9l_UqFpA7vwQhnw0nbh73rXOX2TUDCUqL4ThKU5Z9Pd-eZCEOatKe0mJTpQ00XGACBME_6ojCdfNIJr84Y_IpGKvkAEksn9w",
#       "use": "sig",
#       "kid": "87bbe0815b064e6d449cac999f0e50e72a3e4374",
#       "e": "AQAB",
#       "alg": "RS256",
#       "kty": "RSA"
#     }
#   ]
# }

# -------------------------------------------------------------------------------------------
# Replace this with your actual token.
# This sample token contains a kid that does not match any of the above Google public keys.
# -------------------------------------------------------------------------------------------
$token = "eyJhbGciOiJSUzI1NiIsImtpZCI6IjQyZmY5MGQ3ZDM0OGM5NzM4MWE3YzExOWVmMWY1MzI0ZWEzZjViZWIifQ.eyJpc3MiOiJodHRwczovL2FjY291bnRzLmdvb2dsZS5jb20iLCJzdWIiOiIxMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExIiwiaWF0IjoxNjExMTE1MTQzLCJleHAiOjE2MTEyMDE1NDMsImF1ZCI6IjQyOTc1NzExNTE0ODg0OSJ9.pLem5i0bx3M7lJYj7jKv2Nq7c07X5YpZz-x1uM5RniW-v4LsX-lKIVvOq2x3-WoPqkzLXJfP0kG0dx1uD2q1NfFQK60YwKH4FnFtB6INnUP1dRVpP9_pTTKyAE28I3s5Tay4PbPdrCl7ZLCIJzCfpCW1TiWeVoPjp5HgZKTBHdP_sEkN_yO5dQerQXAkFJkV3kNgF9jI3ayT-KPqOIH6GVoWXjHFDyA2EYgJPEFRo5WSe6XycJ85p5duwT-OoBcb_kJZG9PxYd91eHlPCzp8vGxzIb2dVROCBxyM8e8W0cd9v15hfmpg9R-eG9vCM5y63ZLChZLFeHFx0Pd7hvAqfKg"

$jwt = New-Object Chilkat.Jwt
$header = $jwt.GetHeader($token)

$($header)

# Sample header:
# {"alg":"RS256","kid":"87bbe0815b064e6d449cac999f0e50e72a3e4374"}

# Load the public key matching the "kid" into a Chilkat public key object, then verify..

$json = New-Object Chilkat.JsonObject
$json.Load($header)
$kid = $json.StringOf("kid")

$("kid = " + $kid)

$jsonPubKeys = New-Object Chilkat.JsonObject
$jsonPubKeys.LoadSb($sbPubKeys)

$jsonKey = $jsonPubKeys.FindRecord("keys","kid",$kid,$true)
if ($jsonPubKeys.LastMethodSuccess -eq $false) {
    $("Did not find a matching public key based on the kid.")
    exit
}

$($jsonKey.Emit())

# Load the matching public key into a Chilkat public key object.
$pubKey = New-Object Chilkat.PublicKey
$success = $pubKey.LoadFromString($jsonKey.Emit())

if ($success -eq $false) {
    $($pubKey.LastErrorText)
    exit
}

# ----------------------------------------------------------------------------------------
# Now we can validate the JWT using Google's public key as shown in this example:
# (Except we use the public key obtained as shown above instead of a public key loaded from a PEM file.
# 
# See Verify JWT Using an RSA Public Key