1.OAuth密码模式

2.在VS中创建WebAPI项目

在nuget中安装：

Microsoft.AspNet.WebApi.Owin

Microsoft.Owin.Host.SystemWeb

这两个类库并添加Owin启动类Startup

using System;
using System.Threading.Tasks;
using Microsoft.Owin;
using Owin;
using Microsoft.Owin.Security.OAuth;

[assembly: OwinStartup(typeof(WebAPIOAuth.Startup))]

namespace WebAPIOAuth
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            var OAuthOptions = new OAuthAuthorizationServerOptions
            {
                AllowInsecureHttp = true,
                TokenEndpointPath = new PathString("/token"), //获取 access_token 授权服务请求地址
                AuthorizeEndpointPath = new PathString("/authorize"), //获取 authorization_code 授权服务请求地址
                AccessTokenExpireTimeSpan = TimeSpan.FromSeconds(10), //access_token 过期时间

                Provider = new OpenAuthorizationServerProvider(), //access_token 相关授权服务
            };

            app.UseOAuthBearerTokens(OAuthOptions); //表示 token_type 使用 bearer 方式 不记名令牌验证
        }
    }
}

ConfigureOAuth(IAppBuilder app)方法开启了OAuth服务。简单说一下OAuthAuthorizationServerOptions中各参数的含义：

AllowInsecureHttp：允许客户端一http协议请求；

TokenEndpointPath：token请求的地址，即http://localhost:端口号/token；

AccessTokenExpireTimeSpan ：token过期时间；

Provider ：提供具体的认证策略；

3.继承授权服务OAuthAuthorizationServerProvider类

重载ValidateClientAuthentication方法验证客户端的正确性

重载GrantResourceOwnerCredentials方法实现用户名密码的验证，验证通过后会颁发token。

public class OpenAuthorizationServerProvider : OAuthAuthorizationServerProvider
    {
        /// <summary>
        /// 验证调用端的clientid与clientSecret已验证调用端的合法性(clientid、clientSecret为约定好的字符串)。
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        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);
        }

        /// <summary>
        /// 通过重载GrantResourceOwnerCredentials获取用户名和密码进行认证
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
        {
            //调用后台的登录服务验证用户名与密码
            if (context.UserName != "Admin" || context.Password != "123456")
            {
                context.SetError("invalid_grant", "用户名或密码不正确。");
                return;
            }

            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);
        }
    }

在需要验证的方法处添加[Authorize]标签，当访问此接口时必须通过授权验证才可访问。

以上服务器端代码全部完成。

4.创建新的客户端项目进行测试

添加测试类

class OAuthClientTest
    {
        private HttpClient _httpClient;
        private string token;

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

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

            var parameters = new Dictionary<string, string>();
            parameters.Add("grant_type", "password");
            parameters.Add("username", "Admin");
            parameters.Add("password", "123456");

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

            var response = await _httpClient.PostAsync("OAuthTest/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;
            }
        }

        public async Task Call_WebAPI_By_Resource_Owner_Password_Credentials_Grant()
        {
            if(string.IsNullOrEmpty(token))
                token = await GetAccessToken();
            Console.WriteLine(token);
            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
            Console.WriteLine(await (await _httpClient.GetAsync("OAuthTest/api/Values")).Content.ReadAsStringAsync());
        }
    }

main方法中调用进行测试：

static void Main(string[] args)
        {
            var clientTest = new OAuthClientTest();
            var task = clientTest.Call_WebAPI_By_Resource_Owner_Password_Credentials_Grant();
            task.Wait();
            //var token = clientTest.GetAccessToken();
            //var strToken = token.Result;
            //Console.WriteLine(strToken);
            Console.ReadLine();
        }

结果如下：

其中长串字符为token，"value1, value2"为访问webapi返回的结果，表明访问成功。

参考1：http://www.cnblogs.com/xishuai/p/aspnet-webapi-owin-oauth2.html

参考2：http://www.cnblogs.com/Leo_wl/p/4919783.html