Can you explain what is meant by authentication using bearer tokens?

Bearer tokens are a type of access tokens used for authenticating a user or client when accessing protected resources. In HTTP requests, the token is transmitted in the Authorization header in the following format:

Authorization: Bearer <token>

When the server receives the request, it extracts the token, verifies its validity, and if the token is valid, grants access to the requested resource. This approach is widely used in OAuth 2.0 and other authorization protocols.

Example in C# using HttpClient:

var client = new HttpClient();
client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", "your_token_here");
var response = await client.GetAsync("https://api.example.com/data");

Thus, a bearer token is a kind of access key that must be transmitted in each request to confirm access rights.