Lua

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.

Lua

local chilkat = require("chilkat")

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

local http = chilkat.Http.new()
local sbPubKeys = chilkat.StringBuilder.new()

local success = http:quick_get_sb("https://www.googleapis.com/oauth2/v3/certs", sbPubKeys)
if not success then
    print(http.last_error_text)
    return
end

print(sbPubKeys:get_as_string())

-- 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.
-- -------------------------------------------------------------------------------------------
local token = "eyJhbGciOiJSUzI1NiIsImtpZCI6IjQyZmY5MGQ3ZDM0OGM5NzM4MWE3YzExOWVmMWY1MzI0ZWEzZjViZWIifQ.eyJpc3MiOiJodHRwczovL2FjY291bnRzLmdvb2dsZS5jb20iLCJzdWIiOiIxMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExIiwiaWF0IjoxNjExMTE1MTQzLCJleHAiOjE2MTEyMDE1NDMsImF1ZCI6IjQyOTc1NzExNTE0ODg0OSJ9.pLem5i0bx3M7lJYj7jKv2Nq7c07X5YpZz-x1uM5RniW-v4LsX-lKIVvOq2x3-WoPqkzLXJfP0kG0dx1uD2q1NfFQK60YwKH4FnFtB6INnUP1dRVpP9_pTTKyAE28I3s5Tay4PbPdrCl7ZLCIJzCfpCW1TiWeVoPjp5HgZKTBHdP_sEkN_yO5dQerQXAkFJkV3kNgF9jI3ayT-KPqOIH6GVoWXjHFDyA2EYgJPEFRo5WSe6XycJ85p5duwT-OoBcb_kJZG9PxYd91eHlPCzp8vGxzIb2dVROCBxyM8e8W0cd9v15hfmpg9R-eG9vCM5y63ZLChZLFeHFx0Pd7hvAqfKg"

local jwt = chilkat.Jwt.new()
local header = jwt:get_header(token)

print(header)

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

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

local json = chilkat.JsonObject.new()
json:load(header)
local kid = json:string_of("kid")

print("kid = " .. kid)

local jsonPubKeys = chilkat.JsonObject.new()
jsonPubKeys:load_sb(sbPubKeys)

local jsonKey = jsonPubKeys:find_record("keys", "kid", kid, true)
if not jsonPubKeys.last_method_success then
    print("Did not find a matching public key based on the kid.")
    return
end

print(jsonKey:emit())

-- Load the matching public key into a Chilkat public key object.
local pubKey = chilkat.PublicKey.new()
success = pubKey:load_from_string(jsonKey:emit())

if not success then
    print(pubKey.last_error_text)
    return
end

-- ----------------------------------------------------------------------------------------
-- 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