What is Realm in HTTP Authentication?

In HTTP authentication, a realm is a string identifier the server uses to define a protected area or space on the server that requires authentication. When the server responds to a client with a request for authentication (usually in response to an unauthorized access attempt), it sends back a 401 status code and a "WWW-Authenticate" header that includes the realm.

The realm helps the client understand which credentials to use when accessing the protected resource. For example, if a server has multiple secure areas, the realm distinguishes each one, so the client can present the appropriate username and password.

Realms provide context to users or applications when multiple areas require different authentication methods or credentials, enhancing the ability to manage authentication across different sections of a website or service.