ASP.NET Web API与Owin OAuth：调用与用户相关的Web API

在前一篇博文中，我们通过以 OAuth 的 Client Credential Grant 授权方式（只验证调用客户端，不验证登录用户）拿到的 Access Token ，成功调用了与用户无关的 Web API。

在这篇博文中，我们将以 OAuth 的 Resource Owner Password Credentials Grant 的授权方式（ grant_type=password ）获取 Access Token，并以这个 Token 调用与用户相关的 Web API。

对应的应用场景是：为自家的网站开发手机 App（非第三方 App），只需用户在 App 上登录，无需用户对 App 所能访问的数据进行授权。

根据 OAuth 规范，客户端获取 Access Token 的请求方式如下：

POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded

grant_type=password&username=johndoe&password=A3ddj3w

根据上面的请求方式，在 C# 中用 HttpClient 实现一个简单的客户端，代码如下：

public class OAuthClientTest
{
    private HttpClient _httpClient;

    public OAuthClientTest()
    {
        _httpClient = new HttpClient();
        _httpClient.BaseAddress = new Uri("http://openapi.cnblogs.com");
    } 

    [Fact]
    public async Task Get_Accesss_Token_By_Resource_Owner_Password_Credentials_Grant()
    {
        Console.WriteLine(await GetAccessToken());
    }

    private async Task<string> GetAccessToken()
    {
        var clientId = "1234";
        var clientSecret = "5678";

        var parameters = new Dictionary<string, string>();            
        parameters.Add("grant_type", "password");
        parameters.Add("username", "博客园团队");
        parameters.Add("password", "cnblogs.com");

        _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
            "Basic",
            Convert.ToBase64String(Encoding.ASCII.GetBytes(clientId + ":" + clientSecret))
            );

        var response = await _httpClient.PostAsync("/token", new FormUrlEncodedContent(parameters));
        var responseValue = await response.Content.ReadAsStringAsync();
        if (response.StatusCode == System.Net.HttpStatusCode.OK)
        {
            return JObject.Parse(responseValue)["access_token"].Value<string>();
        }
        else
        {
            Console.WriteLine(responseValue);
            return string.Empty;
        }
    }
}

（注：与之前相比，这里的 client_id/client_secret 改为了 Basic Authorization，以更好的遵循 OAuth 规范）

在服务端，基于 Owin OAuth， 针对 Resource Owner Password Credentials Grant 的授权方式，只需重载 OAuthAuthorizationServerProvider.GrantResourceOwnerCredentials() 方法即可。代码如下：

public class CNBlogsAuthorizationServerProvider : OAuthAuthorizationServerProvider
{
    //...

    public override async Task GrantResourceOwnerCredentials(
        OAuthGrantResourceOwnerCredentialsContext context)
    {
        //调用后台的登录服务验证用户名与密码

        var oAuthIdentity = new ClaimsIdentity(context.Options.AuthenticationType);
        oAuthIdentity.AddClaim(new Claim(ClaimTypes.Name, context.UserName));
        var ticket = new AuthenticationTicket(oAuthIdentity, new AuthenticationProperties());
        context.Validated(ticket);

        await base.GrantResourceOwnerCredentials(context);
    }
}

完整的CNBlogsAuthorizationServerProvider实现代码如下（与之前相比，context.TryGetFormCredentials 改为了 context.TryGetBasicCredentials）：

public class CNBlogsAuthorizationServerProvider : OAuthAuthorizationServerProvider
{
    public override async Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
    {
        string clientId;
        string clientSecret;
        context.TryGetBasicCredentials(out clientId, out clientSecret);

        if (clientId == "1234"
            && clientSecret == "5678")
        {
            context.Validated(clientId);
        }

        await base.ValidateClientAuthentication(context);
    }

    public override async Task GrantClientCredentials(OAuthGrantClientCredentialsContext context)
    {
        var oAuthIdentity = new ClaimsIdentity(context.Options.AuthenticationType);
        var ticket = new AuthenticationTicket(oAuthIdentity, new AuthenticationProperties());
        context.Validated(ticket);

        await base.GrantClientCredentials(context);
    }

    public override async Task GrantResourceOwnerCredentials(
        OAuthGrantResourceOwnerCredentialsContext context)
    {
        //调用后台的登录服务验证用户名与密码

        var oAuthIdentity = new ClaimsIdentity(context.Options.AuthenticationType);
        oAuthIdentity.AddClaim(new Claim(ClaimTypes.Name, context.UserName));
        var ticket = new AuthenticationTicket(oAuthIdentity, new AuthenticationProperties());
        context.Validated(ticket);

        await base.GrantResourceOwnerCredentials(context);
    }
}

CNBlogsAuthorizationServerProvider