Create your own conference system. Part - 1

Creating simple chat via SignalR

Simple demo how it will looks like

First of all we should think about project's folder structure. I will show you my view to it:

Create and configure Asp .Net Core Web application

Lets start from creating .Net Core Web application. It is very easy just follow steps bellow.

• Open Visual Studio
• Create new project and call it ConferenceSystem.Api
• Web\Asp .net core web application
• Type the name of our system: ConferenceSystem.Api. Don't forget follow the structure I mentioned above
• Choose net core 2.2 and empty application, with No Authentication

After this steps empty application will be created by Visual Studio

.Net Core and JWT Authentication

For supporting JWT authentication in .Net Core, we should modify Startup class. But firstly we need to add configuration to appsettings.json

Code explanation

• SecurityKey - this key need to encrypt you JWT
• Issuer - is the server that create the token
• Audience - token receipt
• Last two fields it is an expiration time

For simplifying to work with this setting lets add JWTSettings class.

Lets take a look Startup class and ConfigureServices method

Here you can see how we extract JWT configuration section and deserialize it to JwtSettings class. Then we add Authentication and JwtBearer services. In JwtBearer we configure TokenValidationParameters accordingly configuration from appsettings.json add AuthenticationFailed 'interceptor' where we validate is exception SecurityTokenExpiredException then add Token-Expired header. Token-Expired header allow us to add possibilities to token refresh support.
Since we will use external clients and clients will have other IP addresses we should configure CORS policy. From MSDN: Using CORS, a server can explicitly allow some cross-origin requests while rejecting others.

For turn on our modification we should add Authentication and CORS middleware

Excellent, we have configured our application for supporting JWT authentication, so lets dive more deeply and implement infrastructure for Authentication.

Add secure Api endpoint

I won't to use default UserManager for implementing authentication managing it is not interesting, more exciting to create it from scratch, probably it won't have all possibilities, but for our system, its more than enough.

For working with authenticated user we add Userclass

Then for handling users we need to add service UserService this service will responsible for creating users, validating password and etc.

Code explanation

In current step we won't to add data base support and will use List for keeping users. CreateUserDto just DTO for creating a user. Pay attention to CreateSalt and CreatePassword methods. As you can see every user has its own salt and we should not keep 'clean' password we should keep password's hash

On the next step we need to add some classes and TokenService this service will accountable to create JWT tokens. Firstly take a look across the code and bellow you will find explanation

Code explanation

• JwtToken - represents simple class for transferring to client
• JwtRefreshToken - keeps some information for validating refresh token. This class will be kept inside DataBase/InMemoryDataBase, for client should be send only refresh token value
• TokenService - are further explanation bellow

Well, lets take a look by methods. CreateToken this method creates JWT token and add UserId to Claims. We can extract it from JWT (method: GetUserIdFromExpiredToken) for some reason like authorization or use it due to refreshing token stage. Next method GenerateRefreshToken uses for creating JwtRefreshToken Method GetUserIdFromExpiredToken this method we can split for two parts: first part - here we validate is token valid or not. This code pretty much the same as validation in Startup class except for expire date validation. If token valid we extract ClaimPrincipals than find UserId. AddRefreshTokenAsync and GetRefreshTokenAsync here we add and extract refresh token from storage.

Add the AuthenticationManager class. This class accountable for authentication like a facade combines IUserService and ITokenService

You can see here when token refreshed AuthenticationManager extract UserId then validate is tuple of <UserId, RefreshToken> exists and refresh token is not expired AuthenticationManager generate newJwtToken. Other interesting method is GetCurrentUser. This method is used for retrieving user from request, for doing that we should add IHttpContextAccessor to constructor.

One of the last we need to add the AuthenticationController

AuthenticationController does not catch any exceptions, does not response correct exception texts, but it is example project and it is the only first part, in the future, we will fix it.

Last but not least we need to add our dependencies to DI container in Startup. in the ent of configureService add the following rows:
services.AddScoped<IAuthenticationManager, AuthenticationManager>();
services.AddScoped<ITokenService, TokenService>();
services.AddScoped<IUserService, UserService>();
services.AddHttpContextAccessor();


Lets validate how does it work.

• Authenticate

  

• Refresh token

  

• Register

  

Add simple chat implementation

Firstly we need to create class which will be inherited from Hub

Code explanation

• [Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme)] - here we specified access only for authorized users.
• ConnectedClients - dictionary where we will keep all connected users, it can be replaced for DataBase for example. This dictionary contains connection ids via user since one user can cbe connected with different devices.
• SendMessage - this method are responsible for communication between clients, will will call this method for send message to recipients.
• RequestConnectedClients - this method response to caller only, and return all connected users.
• OnConnectedAsync - this standard method is fired when someone connected to the conference hub. When someone connected to we pup this connection id to the dictionary. Then call OnConnectedUser method for all connected users for notified that the user is online
• OnDisconnectedAsync - the same as above but fired when user lose connection.

For allowing this hub works we should add some changes to Startup class

In JwtBearerEvents we should add following rows

This code validate is connection to the hub and then retrieve token(which should be sent as parameter) and set this token to context.

Last few thinks, add services.AddSignalR(); to service collection and add app.UseSignalR(routes => { routes.MapHub<ConferenceHub>("/conference"); }) to execution middleware.

In the end we will add UserController for retrieve user information.

That's it, we have finished first part where we have implements back-end part for our future conference system.