I feel like I'm taking crazy pills here. Usually there's always a million library and samples floating around the web for any given task. I'm trying to implement authentication with a Google "Service Account" by use of JSON Web Tokens (JWT) as described here.
However there is only client libraries in PHP, Python, and Java. Even searching for JWT examples outside of Google's authentication, there is only crickets and drafts on the JWT concept. Is this really so new and possibly a Google proprietary system?
The java sample which is the closest I could manage to interpret looks pretty intensive and intimidating. There's got to be something out there in C# that I could at least start with. Any help with this would be great!
Take a look at Google Client Library for .NET.
It would be better to use standard and famous libraries instead of writing the code from scratch.
Using these libraries you can generate a JWT token and sign it using RS256 as below.
public string GenerateJWTToken(string rsaPrivateKey)
{
var rsaParams = GetRsaParameters(rsaPrivateKey);
var encoder = GetRS256JWTEncoder(rsaParams);
// create the payload according to the Google's doc
var payload = new Dictionary<string, object>
{
{ "iss", ""},
{ "sub", "" },
// and other key-values according to the doc
};
// add headers. 'alg' and 'typ' key-values are added automatically.
var header = new Dictionary<string, object>
{
{ "kid", "{your_private_key_id}" },
};
var token = encoder.Encode(header,payload, new byte[0]);
return token;
}
private static IJwtEncoder GetRS256JWTEncoder(RSAParameters rsaParams)
{
var csp = new RSACryptoServiceProvider();
csp.ImportParameters(rsaParams);
var algorithm = new RS256Algorithm(csp, csp);
var serializer = new JsonNetSerializer();
var urlEncoder = new JwtBase64UrlEncoder();
var encoder = new JwtEncoder(algorithm, serializer, urlEncoder);
return encoder;
}
private static RSAParameters GetRsaParameters(string rsaPrivateKey)
{
var byteArray = Encoding.ASCII.GetBytes(rsaPrivateKey);
using (var ms = new MemoryStream(byteArray))
{
using (var sr = new StreamReader(ms))
{
// use Bouncy Castle to convert the private key to RSA parameters
var pemReader = new PemReader(sr);
var keyPair = pemReader.ReadObject() as AsymmetricCipherKeyPair;
return DotNetUtilities.ToRSAParameters(keyPair.Private as RsaPrivateCrtKeyParameters);
}
}
}
ps: the RSA private key should have the following format:
-----BEGIN RSA PRIVATE KEY----- {base64 formatted value} -----END RSA PRIVATE KEY-----
Here is another REST-only working example for Google Service Accounts accessing G Suite Users and Groups, authenticating through JWT. This was only possible through reflection of Google libraries, since Google documentation of these APIs are beyond terrible. Anyone used to code in MS technologies will have a hard time figuring out how everything goes together in Google services.
$iss = "<name>@<serviceaccount>.iam.gserviceaccount.com"; # The email address of the service account.
$sub = "[email protected]"; # The user to impersonate (required).
$scope = "https://www.googleapis.com/auth/admin.directory.user.readonly https://www.googleapis.com/auth/admin.directory.group.readonly";
$certPath = "D:\temp\mycertificate.p12";
$grantType = "urn:ietf:params:oauth:grant-type:jwt-bearer";
# Auxiliary functions
function UrlSafeEncode([String] $Data) {
return $Data.Replace("=", [String]::Empty).Replace("+", "-").Replace("/", "_");
}
function UrlSafeBase64Encode ([String] $Data) {
return (UrlSafeEncode -Data ([Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes($Data))));
}
function KeyFromCertificate([System.Security.Cryptography.X509Certificates.X509Certificate2] $Certificate) {
$privateKeyBlob = $Certificate.PrivateKey.ExportCspBlob($true);
$key = New-Object System.Security.Cryptography.RSACryptoServiceProvider;
$key.ImportCspBlob($privateKeyBlob);
return $key;
}
function CreateSignature ([Byte[]] $Data, [System.Security.Cryptography.X509Certificates.X509Certificate2] $Certificate) {
$sha256 = [System.Security.Cryptography.SHA256]::Create();
$key = (KeyFromCertificate $Certificate);
$assertionHash = $sha256.ComputeHash($Data);
$sig = [Convert]::ToBase64String($key.SignHash($assertionHash, "2.16.840.1.101.3.4.2.1"));
$sha256.Dispose();
return $sig;
}
function CreateAssertionFromPayload ([String] $Payload, [System.Security.Cryptography.X509Certificates.X509Certificate2] $Certificate) {
$header = @"
{"alg":"RS256","typ":"JWT"}
"@;
$assertion = New-Object System.Text.StringBuilder;
$assertion.Append((UrlSafeBase64Encode $header)).Append(".").Append((UrlSafeBase64Encode $Payload)) | Out-Null;
$signature = (CreateSignature -Data ([System.Text.Encoding]::ASCII.GetBytes($assertion.ToString())) -Certificate $Certificate);
$assertion.Append(".").Append((UrlSafeEncode $signature)) | Out-Null;
return $assertion.ToString();
}
$baseDateTime = New-Object DateTime(1970, 1, 1, 0, 0, 0, [DateTimeKind]::Utc);
$timeInSeconds = [Math]::Truncate([DateTime]::UtcNow.Subtract($baseDateTime).TotalSeconds);
$jwtClaimSet = @"
{"scope":"$scope","email_verified":false,"iss":"$iss","sub":"$sub","aud":"https://oauth2.googleapis.com/token","exp":$($timeInSeconds + 3600),"iat":$timeInSeconds}
"@;
$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2($certPath, "notasecret", [System.Security.Cryptography.X509Certificates.X509KeyStorageFlags]::Exportable);
$jwt = CreateAssertionFromPayload -Payload $jwtClaimSet -Certificate $cert;
# Retrieve the authorization token.
$authRes = Invoke-WebRequest -Uri "https://oauth2.googleapis.com/token" -Method Post -ContentType "application/x-www-form-urlencoded" -UseBasicParsing -Body @"
assertion=$jwt&grant_type=$([Uri]::EscapeDataString($grantType))
"@;
$authInfo = ConvertFrom-Json -InputObject $authRes.Content;
$resUsers = Invoke-WebRequest -Uri "https://www.googleapis.com/admin/directory/v1/users?domain=<required_domain_name_dont_trust_google_documentation_on_this>" -Method Get -Headers @{
"Authorization" = "$($authInfo.token_type) $($authInfo.access_token)"
}
$users = ConvertFrom-Json -InputObject $resUsers.Content;
$users.users | ft primaryEmail, isAdmin, suspended;
Here is a working example:
http://zavitax.wordpress.com/2012/12/17/logging-in-with-google-service-account-in-c-jwt/
It took quite some time to collect the pieces scattered over the web, the docs are rather incomplete...
This is my implementation of (Google) JWT Validation in .NET. It is based on other implementations on Stack Overflow and GitHub gists.
using Microsoft.IdentityModel.Tokens;
using System;
using System.Collections.Generic;
using System.IdentityModel.Tokens.Jwt;
using System.Linq;
using System.Net.Http;
using System.Security.Claims;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;
namespace QuapiNet.Service
{
public class JwtTokenValidation
{
public async Task<Dictionary<string, X509Certificate2>> FetchGoogleCertificates()
{
using (var http = new HttpClient())
{
var response = await http.GetAsync("https://www.googleapis.com/oauth2/v1/certs");
var dictionary = await response.Content.ReadAsAsync<Dictionary<string, string>>();
return dictionary.ToDictionary(x => x.Key, x => new X509Certificate2(Encoding.UTF8.GetBytes(x.Value)));
}
}
private string CLIENT_ID = "xxx.apps.googleusercontent.com";
public async Task<ClaimsPrincipal> ValidateToken(string idToken)
{
var certificates = await this.FetchGoogleCertificates();
TokenValidationParameters tvp = new TokenValidationParameters()
{
ValidateActor = false, // check the profile ID
ValidateAudience = true, // check the client ID
ValidAudience = CLIENT_ID,
ValidateIssuer = true, // check token came from Google
ValidIssuers = new List<string> { "accounts.google.com", "https://accounts.google.com" },
ValidateIssuerSigningKey = true,
RequireSignedTokens = true,
IssuerSigningKeys = certificates.Values.Select(x => new X509SecurityKey(x)),
IssuerSigningKeyResolver = (token, securityToken, kid, validationParameters) =>
{
return certificates
.Where(x => x.Key.ToUpper() == kid.ToUpper())
.Select(x => new X509SecurityKey(x.Value));
},
ValidateLifetime = true,
RequireExpirationTime = true,
ClockSkew = TimeSpan.FromHours(13)
};
JwtSecurityTokenHandler jsth = new JwtSecurityTokenHandler();
SecurityToken validatedToken;
ClaimsPrincipal cp = jsth.ValidateToken(idToken, tvp, out validatedToken);
return cp;
}
}
}
Note that, in order to use it, you need to add a reference to the NuGet package System.Net.Http.Formatting.Extension. Without this, the compiler will not recognize the ReadAsAsync<> method.
Here is the list of classes and functions:
open System
open System.Collections.Generic
open System.Linq
open System.Threading.Tasks
open Microsoft.AspNetCore.Mvc
open Microsoft.Extensions.Logging
open Microsoft.AspNetCore.Authorization
open Microsoft.AspNetCore.Authentication
open Microsoft.AspNetCore.Authentication.JwtBearer
open Microsoft.IdentityModel.Tokens
open System.IdentityModel.Tokens
open System.IdentityModel.Tokens.Jwt
open Microsoft.IdentityModel.JsonWebTokens
open System.Text
open Newtonsoft.Json
open System.Security.Claims
let theKey = "VerySecretKeyVerySecretKeyVerySecretKey"
let securityKey = SymmetricSecurityKey(Encoding.UTF8.GetBytes(theKey))
let credentials = SigningCredentials(securityKey, SecurityAlgorithms.RsaSsaPssSha256)
let expires = DateTime.UtcNow.AddMinutes(123.0) |> Nullable
let token = JwtSecurityToken(
"lahoda-pro-issuer",
"lahoda-pro-audience",
claims = null,
expires = expires,
signingCredentials = credentials
)
let tokenString = JwtSecurityTokenHandler().WriteToken(token)
I've never used it but there is a JWT implementation on NuGet.
Package: https://nuget.org/packages/JWT
Source: https://github.com/johnsheehan/jwt
.NET 4.0 compatible: https://www.nuget.org/packages/jose-jwt/
You can also go here: https://jwt.io/ and click "libraries".
After all these months have passed after the original question, it's now worth pointing out that Microsoft has devised a solution of their own. See http://blogs.msdn.com/b/vbertocci/archive/2012/11/20/introducing-the-developer-preview-of-the-json-web-token-handler-for-the-microsoft-net-framework-4-5.aspx for details.
Source: Stackoverflow.com