Identity Server 4 Authorization Code Flow example
I'm trying to implement Identity Server 4 with AspNet Core using Authorization Code Flow.
The thing is, the IdentityServer4 repository on github have several samples, but none with Authorization Code Flow.
Does anyone have a sample on how to implement Authorization Code Flow with Identity Server 4 and a Client in MVC consuming it?
Answer
Here's an implementation of an Authorization Code Flow with Identity Server 4 and an MVC client to consume it.
IdentityServer4 can use a client.cs file to register our MVC client, it's ClientId, ClientSecret, allowed grant types (Authorization Code in this case), and the RedirectUri of our client:
public class Clients
{
public static IEnumerable<Client> Get()
{
var secret = new Secret { Value = "mysecret".Sha512() };
return new List<Client> {
new Client {
ClientId = "authorizationCodeClient2",
ClientName = "Authorization Code Client",
ClientSecrets = new List<Secret> { secret },
Enabled = true,
AllowedGrantTypes = new List<string> { "authorization_code" }, //DELTA //IdentityServer3 wanted Flow = Flows.AuthorizationCode,
RequireConsent = true,
AllowRememberConsent = false,
RedirectUris =
new List<string> {
"http://localhost:5436/account/oAuth2"
},
PostLogoutRedirectUris =
new List<string> {"http://localhost:5436"},
AllowedScopes = new List<string> {
"api"
},
AccessTokenType = AccessTokenType.Jwt
}
};
}
}
This class is referenced in the ConfigurationServices method of the Startup.cs in the IdentityServer4 project:
public void ConfigureServices(IServiceCollection services)
{
////Grab key for signing JWT signature
////In prod, we'd get this from the certificate store or similar
var certPath = Path.Combine(PlatformServices.Default.Application.ApplicationBasePath, "SscSign.pfx");
var cert = new X509Certificate2(certPath);
// configure identity server with in-memory stores, keys, clients and scopes
services.AddDeveloperIdentityServer(options =>
{
options.IssuerUri = "SomeSecureCompany";
})
.AddInMemoryScopes(Scopes.Get())
.AddInMemoryClients(Clients.Get())
.AddInMemoryUsers(Users.Get())
.SetSigningCredential(cert);
services.AddMvc();
}
For reference, here are the Users and Scopes classes referenced above:
public static class Users
{
public static List<InMemoryUser> Get()
{
return new List<InMemoryUser> {
new InMemoryUser {
Subject = "1",
Username = "user",
Password = "pass123",
Claims = new List<Claim> {
new Claim(ClaimTypes.GivenName, "GivenName"),
new Claim(ClaimTypes.Surname, "surname"), //DELTA //.FamilyName in IdentityServer3
new Claim(ClaimTypes.Email, "[email protected]"),
new Claim(ClaimTypes.Role, "Badmin")
}
}
};
}
}
public class Scopes
{
// scopes define the resources in your system
public static IEnumerable<Scope> Get()
{
return new List<Scope> {
new Scope
{
Name = "api",
DisplayName = "api scope",
Type = ScopeType.Resource,
Emphasize = false,
}
};
}
}
The MVC application requires two controller methods. The first method kicks-off the Service Provider (SP-Initiated) workflow. It creates a State value, saves it in cookie-based authentication middleware, and then redirects the browser to the IdentityProvider (IdP) - our IdentityServer4 project in this case.
public ActionResult SignIn()
{
var state = Guid.NewGuid().ToString("N");
//Store state using cookie-based authentication middleware
this.SaveState(state);
//Redirect to IdP to get an Authorization Code
var url = idPServerAuthUri +
"?client_id=" + clientId +
"&response_type=" + response_type +
"&redirect_uri=" + redirectUri +
"&scope=" + scope +
"&state=" + state;
return this.Redirect(url); //performs a GET
}
For reference, here are the constants and SaveState method utilized above:
//Client and workflow values
private const string clientBaseUri = @"http://localhost:5436";
private const string validIssuer = "SomeSecureCompany";
private const string response_type = "code";
private const string grantType = "authorization_code";
//IdentityServer4
private const string idPServerBaseUri = @"http://localhost:5000";
private const string idPServerAuthUri = idPServerBaseUri + @"/connect/authorize";
private const string idPServerTokenUriFragment = @"connect/token";
private const string idPServerEndSessionUri = idPServerBaseUri + @"/connect/endsession";
//These are also registered in the IdP (or Clients.cs of test IdP)
private const string redirectUri = clientBaseUri + @"/account/oAuth2";
private const string clientId = "authorizationCodeClient2";
private const string clientSecret = "mysecret";
private const string audience = "SomeSecureCompany/resources";
private const string scope = "api";
//Store values using cookie-based authentication middleware
private void SaveState(string state)
{
var tempId = new ClaimsIdentity("TempCookie");
tempId.AddClaim(new Claim("state", state));
this.Request.GetOwinContext().Authentication.SignIn(tempId);
}
The second MVC action method is called by IdenityServer4 after the user enters their credentials and checks any authorization boxes. The action method:
- Grabs the Authorization Code and State from the query string
- Validates State
- POSTs back to IdentityServer4 to exchange the Authorization Code for an Access Token
Here's the method:
[HttpGet]
public async Task<ActionResult> oAuth2()
{
var authorizationCode = this.Request.QueryString["code"];
var state = this.Request.QueryString["state"];
//Defend against CSRF attacks http://www.twobotechnologies.com/blog/2014/02/importance-of-state-in-oauth2.html
await ValidateStateAsync(state);
//Exchange Authorization Code for an Access Token by POSTing to the IdP's token endpoint
string json = null;
using (var client = new HttpClient())
{
client.BaseAddress = new Uri(idPServerBaseUri);
var content = new FormUrlEncodedContent(new[]
{
new KeyValuePair<string, string>("grant_type", grantType)
,new KeyValuePair<string, string>("code", authorizationCode)
,new KeyValuePair<string, string>("redirect_uri", redirectUri)
,new KeyValuePair<string, string>("client_id", clientId) //consider sending via basic authentication header
,new KeyValuePair<string, string>("client_secret", clientSecret)
});
var httpResponseMessage = client.PostAsync(idPServerTokenUriFragment, content).Result;
json = httpResponseMessage.Content.ReadAsStringAsync().Result;
}
//Extract the Access Token
dynamic results = JsonConvert.DeserializeObject<dynamic>(json);
string accessToken = results.access_token;
//Validate token crypto
var claims = ValidateToken(accessToken);
//What is done here depends on your use-case.
//If the accessToken is for calling a WebAPI, the next few lines wouldn't be needed.
//Build claims identity principle
var id = new ClaimsIdentity(claims, "Cookie"); //"Cookie" matches middleware named in Startup.cs
//Sign into the middleware so we can navigate around secured parts of this site (e.g. [Authorized] attribute)
this.Request.GetOwinContext().Authentication.SignIn(id);
return this.Redirect("/Home");
}
Checking that the State received is what you expected helps defend against CSRF attacks: http://www.twobotechnologies.com/blog/2014/02/importance-of-state-in-oauth2.html
This ValidateStateAsync method compares the received State to what was saved off in the cookie middleware:
private async Task<AuthenticateResult> ValidateStateAsync(string state)
{
//Retrieve state value from TempCookie
var authenticateResult = await this.Request
.GetOwinContext()
.Authentication
.AuthenticateAsync("TempCookie");
if (authenticateResult == null)
throw new InvalidOperationException("No temp cookie");
if (state != authenticateResult.Identity.FindFirst("state").Value)
throw new InvalidOperationException("invalid state");
return authenticateResult;
}
This ValidateToken method uses Microsoft's System.IdentityModel and System.IdentityModel.Tokens.Jwt libraries to check that JWT is properly signed.
private IEnumerable<Claim> ValidateToken(string token)
{
//Grab certificate for verifying JWT signature
//IdentityServer4 also has a default certificate you can might reference.
//In prod, we'd get this from the certificate store or similar
var certPath = Path.Combine(Server.MapPath("~/bin"), "SscSign.pfx");
var cert = new X509Certificate2(certPath);
var x509SecurityKey = new X509SecurityKey(cert);
var parameters = new TokenValidationParameters
{
RequireSignedTokens = true,
ValidAudience = audience,
ValidIssuer = validIssuer,
IssuerSigningKey = x509SecurityKey,
RequireExpirationTime = true,
ClockSkew = TimeSpan.FromMinutes(5)
};
//Validate the token and retrieve ClaimsPrinciple
var handler = new JwtSecurityTokenHandler();
SecurityToken jwt;
var id = handler.ValidateToken(token, parameters, out jwt);
//Discard temp cookie and cookie-based middleware authentication objects (we just needed it for storing State)
this.Request.GetOwinContext().Authentication.SignOut("TempCookie");
return id.Claims;
}
A working solution containing these source files resides on GitHub at https://github.com/bayardw/IdentityServer4.Authorization.Code