docs(authentication): update construction service declarations to match current implementation

Author: Re9iNee

content/security/authentication.md

@@ -111,7 +111,7 @@ import { UsersService } from '../users/users.service';
 
 @Injectable()
 export class AuthService {
-  constructor(private usersService: UsersService) {}
+  constructor(private readonly usersService: UsersService) {}
 
   async signIn(username: string, pass: string): Promise<any> {
     const user = await this.usersService.findOne(username);
@@ -188,7 +188,7 @@ import { AuthService } from './auth.service';
 
 @Controller('auth')
 export class AuthController {
-  constructor(private authService: AuthService) {}
+  constructor(private readonly authService: AuthService) {}
 
   @HttpCode(HttpStatus.OK)
   @Post('login')
@@ -373,7 +373,7 @@ import { Request } from 'express';
 
 @Injectable()
 export class AuthGuard implements CanActivate {
-  constructor(private jwtService: JwtService) {}
+  constructor(private readonly jwtService: JwtService) {}
 
   async canActivate(context: ExecutionContext): Promise<boolean> {
     const request = context.switchToHttp().getRequest();
@@ -425,7 +425,7 @@ import { AuthService } from './auth.service';
 
 @Controller('auth')
 export class AuthController {
-  constructor(private authService: AuthService) {}
+  constructor(private readonly authService: AuthService) {}
 
   @HttpCode(HttpStatus.OK)
   @Post('login')
@@ -506,7 +506,7 @@ Lastly, we need the `AuthGuard` to return `true` when the `"isPublic"` metadata
 ```typescript
 @Injectable()
 export class AuthGuard implements CanActivate {
-  constructor(private jwtService: JwtService, private reflector: Reflector) {}
+  constructor(private readonly jwtService: JwtService, private reflector: Reflector) {}
 
   async canActivate(context: ExecutionContext): Promise<boolean> {
     const isPublic = this.reflector.getAllAndOverride<boolean>(IS_PUBLIC_KEY, [