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

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

Answer 1

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] ");