Session Value

While it's technically possible to send an ASP.Net session cookie from Angular to an ASP.Net Core Web API, it's strongly discouraged due to security concerns and limitations.

Limitations:

• Stateless nature of Web APIs: ASP.Net Core Web APIs are designed to be stateless, meaning they don't maintain user sessions on the server-side like traditional ASP.Net applications.
• Cookie management complexity: You'll need to handle cookie persistence and synchronization between Angular and ASP.Net Core carefully, which can be complex and error-prone.

Recommended Alternatives:

Instead of relying on ASP.Net session cookies, consider these more secure and recommended approaches:

• Token-based authentication: Implement token-based authentication using technologies like JWT (JSON Web Token). Store the token securely on the client-side (e.g., in local storage) and send it with each request to your API. The API can then validate the token to authenticate the user.
• Server-side session management: If you need to maintain user state on the server, consider using a distributed session store like Redis or Azure Cache for Redis. This allows you to store session data centrally and access it from both your Angular app and ASP.Net Core Web API.

Please try below example 

public void ConfigureServices(IServiceCollection services)
{
    // Other services and configurations

    services.AddDistributedMemoryCache();

    services.AddSession(options =>
    {
        options.Cookie.Name = ".AspNetCore.Session";
        options.IdleTimeout = TimeSpan.FromMinutes(30); // Set the session timeout as needed
        options.Cookie.HttpOnly = true;
        options.Cookie.IsEssential = true; // Required to avoid GDPR consent issues
    });
}

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';

@Injectable()
export class ApiService {
  private apiUrl = 'https://your-api-url.com'; // Replace with your ASP.NET Core Web API URL

  constructor(private http: HttpClient) {}

  // Function to get session value from the ASP.NET Core Web API
  getSessionValue() {
    // Get the ASP.NET session cookie from the browser
    const aspSessionCookie = document.cookie
      .split(';')
      .find((cookie) => cookie.trim().startsWith('.AspNetCore.Session='));

    // Set the ASP.NET session cookie in the request headers
    const headers = new HttpHeaders({
      'Content-Type': 'application/json',
      Cookie: aspSessionCookie,
    });

    // Send a GET request to the API to get the session value
    return this.http.get(`${this.apiUrl}/api/sessionValue`, { headers });
  }
}

[ApiController]
[Route("api/[controller]")]
public class SessionController : ControllerBase
{
    [HttpGet("sessionValue")]
    public IActionResult GetSessionValue()
    {
        // Retrieve the session value from ASP.NET Core session
        var sessionValue = HttpContext.Session.GetString("your-session-key");

        return Ok(sessionValue);
    }
}