ASP.NET Core 5 MVC web application - Login via xamarin

Question

I've developed my ASP.NET Core 5 MVC application with "Individual Login". Registering and logging within the app works fine.

Now I want to log in to my MVC web application with an API for my Xamarin App. From what I've read "JWT" should be used. I want to use as much "standard" in the backend as possible, ideally using standard APIs.

Unfortunately, all the sites I've tried could not help me (solution broken, non-existing urls,....).

Could somebody please post me a working tutorial or an example for the backend please.

Thanks, Jeppen

This helped a lot https://stackoverflow.com/questions/40281050/jwt-authentication-for-asp-net-web-api — Jeppen, Dec 28 '20 at 16:44

Karney. · Accepted Answer · 2020-12-30T01:31:41.487

From api, you can configure the jwt authentication as this.

In Startup

 public void ConfigureServices(IServiceCollection services)
 {
     services.AddAuthentication(x =>
     {
         x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
         x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
     })
     .AddJwtBearer(o =>
     {

         o.TokenValidationParameters = new TokenValidationParameters
         {
             NameClaimType = JwtClaimTypes.Name,
             RoleClaimType = JwtClaimTypes.Role,

             //The previous three items are required
             ValidIssuer = "http://localhost:5000",
             ValidAudience = "api",
             IssuerSigningKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes("this is a long key"))

             /***********************************default TokenValidationParameters parameter***********************************/
             // RequireSignedTokens = true,
             // SaveSigninToken = false,
             // ValidateActor = false,

         };

     });
     services.AddControllers();
 }

 public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
 {
     //...
     app.UseRouting();
     app.UseAuthentication();
     app.UseAuthorization();
     //...
 }

Apply for a token, generate a string token in the action.

 public IActionResult Authenticate()
 {

     var tokenHandler = new JwtSecurityTokenHandler();
     var key = Encoding.ASCII.GetBytes("this is a long key");
     var authTime = DateTime.UtcNow;
     var expiresAt = authTime.AddDays(7);
     var tokenDescriptor = new SecurityTokenDescriptor
     {
         Subject = new ClaimsIdentity(new Claim[]
         {
             new Claim(JwtClaimTypes.Audience,"api"),
             new Claim(JwtClaimTypes.Issuer,"http://localhost:5000"),
             new Claim(JwtClaimTypes.Id, "10"),
             new Claim(JwtClaimTypes.Name, "my name"),
             new Claim(JwtClaimTypes.Email, "email"),
         }),
         Expires = expiresAt,
         SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(key), SecurityAlgorithms.HmacSha256Signature)
     };
     var token = tokenHandler.CreateToken(tokenDescriptor);
     var tokenString = tokenHandler.WriteToken(token);

     return Ok(tokenString);
 }

Xamarin App receives token and save it. When Xamarin App access the authorized resource, it can carray this token with this header.

     var client = new HttpClient();
     var token = client.GetAsync("[url that get the token] ");

     client.DefaultRequestHeaders.Add("Authorization", $"Bearer {token}");
     client.GetAsync("[url that get the authorized resource] ");

Thank you very much, the first time my app is creating a token. But when I run my site, I get a blank page. In the developper tools, I get a 401 Unauthorized. Do you have any idea? — Jeppen, Dec 29 '20 at 13:41
Make sure that configuration in the startup is the same as the configuration of the token (Audience, Issuer, IssuerSigningKey). — Karney., Dec 30 '20 at 01:40

ASP.NET Core 5 MVC web application - Login via xamarin

1 Answers1