Update authentication.py Code Simplification

Reduced redundant checks in the authenticate method by combining the conditions for the length of auth.
Removed the unnecessary elif in favor of an if to make the code flow clearer

Author: Codex-v

rest_framework/authentication.py

@@ -150,10 +150,10 @@ def dummy_get_response(request):  # pragma: no cover
 
 class TokenAuthentication(BaseAuthentication):
     """
-    Simple token based authentication.
+    Simple token-based authentication.
 
     Clients should authenticate by passing the token key in the "Authorization"
-    HTTP header, prepended with the string "Token ".  For example:
+    HTTP header, prepended with the string "Token ". For example:
 
         Authorization: Token 401f7ac837da42b97f613d789819ff93537bee6a
     """
@@ -167,31 +167,19 @@ def get_model(self):
         from rest_framework.authtoken.models import Token
         return Token
 
-    """
-    A custom token model may be used, but must have the following properties.
-
-    * key -- The string identifying the token
-    * user -- The user to which the token belongs
-    """
-
     def authenticate(self, request):
         auth = get_authorization_header(request).split()
 
-        if not auth or auth[0].lower() != self.keyword.lower().encode():
+        if len(auth) != 2 or auth[0].lower() != self.keyword.lower().encode():
             return None
-
-        if len(auth) == 1:
-            msg = _('Invalid token header. No credentials provided.')
-            raise exceptions.AuthenticationFailed(msg)
-        elif len(auth) > 2:
-            msg = _('Invalid token header. Token string should not contain spaces.')
-            raise exceptions.AuthenticationFailed(msg)
-
+        
+        token = auth[1]
         try:
-            token = auth[1].decode()
+            token = token.decode()
         except UnicodeError:
-            msg = _('Invalid token header. Token string should not contain invalid characters.')
-            raise exceptions.AuthenticationFailed(msg)
+            raise exceptions.AuthenticationFailed(
+                _('Invalid token header. Token string should not contain invalid characters.')
+            )
 
         return self.authenticate_credentials(token)
 
@@ -205,7 +193,7 @@ def authenticate_credentials(self, key):
         if not token.user.is_active:
             raise exceptions.AuthenticationFailed(_('User inactive or deleted.'))
 
-        return (token.user, token)
+        return token.user, token
 
     def authenticate_header(self, request):
         return self.keyword