logout should not return 401 without redirect uri

[ivanjx]

i think this should not return 401 so it wont interfere with the custom errors middleware (see #390)
https://github.com/thomseddon/traefik-forward-auth/blob/master/internal/server.go#L213

[ljluestc]

// In server.go, around line 213
http.HandleFunc("/logout", func(w http.ResponseWriter, r *http.Request) {
    // Get the redirect_uri from query parameters
    redirectUri := r.URL.Query().Get("redirect_uri")
    
    // If redirect_uri is not provided, redirect to a default URL or handle it gracefully
    if redirectUri == "" {
        // Redirect to a default URL or return an informative response
        // This can be any URL or a page showing that logout was successful
        http.Redirect(w, r, "/default-logout-url", http.StatusFound)
        return
    }

    // Your existing logout logic, which can include clearing session cookies, etc.
    // Clear the session or cookies here, depending on your logic
    // Example:
    // http.SetCookie(w, &http.Cookie{
    //     Name:   "auth_token",
    //     Value:  "",
    //     MaxAge: -1,
    // })
    
    // After performing the logout logic, redirect to the provided redirect_uri
    http.Redirect(w, r, redirectUri, http.StatusFound)
})