Add docs from gofiber/fiber@b176062

Author: github-actions[bot]

docs/core/middleware/basicauth.md

@@ -4,9 +4,9 @@ id: basicauth
 
 # BasicAuth
 
-Basic Authentication middleware for [Fiber](https://github.com/gofiber/fiber) that provides HTTP basic auth. It calls the next handler for valid credentials and returns [`401 Unauthorized`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/401) or a custom response for missing or invalid credentials.
+Basic Authentication middleware for [Fiber](https://github.com/gofiber/fiber) that provides HTTP basic auth. It calls the next handler for valid credentials and returns [`401 Unauthorized`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/401) for missing or invalid credentials, [`400 Bad Request`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/400) for malformed `Authorization` headers, or [`431 Request Header Fields Too Large`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/431) when the header exceeds size limits. Credentials may omit Base64 padding as permitted by RFC 7235's `token68` syntax.
 
-The default unauthorized response includes the header `WWW-Authenticate: Basic realm="Restricted", charset="UTF-8"`, sets `Cache-Control: no-store`, and adds a `Vary: Authorization` header.
+The default unauthorized response includes the header `WWW-Authenticate: Basic realm="Restricted", charset="UTF-8"`, sets `Cache-Control: no-store`, and adds a `Vary: Authorization` header. Only the `UTF-8` charset is supported; any other value will panic.
 
 ## Signatures
 
@@ -98,10 +98,11 @@ Users: map[string]string{
 | Next            | `func(fiber.Ctx) bool`     | Next defines a function to skip this middleware when it returns true.                                                                                                   | `nil`                 |
 | Users           | `map[string]string`         | Users maps usernames to **hashed** passwords (e.g. bcrypt, `{SHA256}`). | `map[string]string{}` |
 | Realm           | `string`                    | Realm is a string to define the realm attribute of BasicAuth. The realm identifies the system to authenticate against and can be used by clients to save credentials. | `"Restricted"`        |
-| Charset         | `string`                    | Charset sent in the `WWW-Authenticate` header, so clients know how credentials are encoded. | `"UTF-8"` |
+| Charset         | `string`                    | Charset sent in the `WWW-Authenticate` header. Only `"UTF-8"` is supported (case-insensitive). | `"UTF-8"` |
 | HeaderLimit     | `int`                       | Maximum allowed length of the `Authorization` header. Requests exceeding this limit are rejected. | `8192` |
 | Authorizer      | `func(string, string, fiber.Ctx) bool` | Authorizer defines a function to check the credentials. It will be called with a username, password, and the current context and is expected to return true or false to indicate approval.  | `nil`                 |
 | Unauthorized    | `fiber.Handler`             | Unauthorized defines the response body for unauthorized responses.                                                                                                    | `nil`                 |
+| BadRequest      | `fiber.Handler`             | BadRequest defines the response for malformed `Authorization` headers.                                                                                     | `nil`                 |
 
 ## Default Config
 
@@ -114,5 +115,6 @@ var ConfigDefault = Config{
     HeaderLimit:     8192,
     Authorizer:      nil,
     Unauthorized:    nil,
+    BadRequest:      nil,
 }
 ```