invites: Use check_int_in to validate invite_as.

(cherry picked from commit ea9b05d88a)

zerver/lib/validator.py

@@ -161,6 +161,11 @@ def check_int(var_name: str, val: object) -> int:
 
 
 def check_int_in(possible_values: List[int]) -> Validator[int]:
+    """
+    Assert that the input is an integer and is contained in `possible_values`. If the input is not in
+    `possible_values`, a `ValidationError` is raised containing the failing field's name.
+    """
+
     def validator(var_name: str, val: object) -> int:
         n = check_int(var_name, val)
         if n not in possible_values:

zerver/tests/test_signup.py

@@ -1501,7 +1501,7 @@ class InviteUserTest(InviteUserBase):
         self.login("iago")
         invitee = self.nonreg_email("alice")
         response = self.invite(invitee, ["Denmark"], invite_as=10)
-        self.assert_json_error(response, "Must be invited as an valid type of user")
+        self.assert_json_error(response, "Invalid invite_as")
 
     def test_successful_invite_user_as_guest_from_normal_account(self) -> None:
         self.login("hamlet")

zerver/views/invite.py

@@ -46,7 +46,12 @@ def invite_users_backend(
     invite_expires_in_minutes: Optional[int] = REQ(
         json_validator=check_none_or(check_int), default=INVITATION_LINK_VALIDITY_MINUTES
     ),
-    invite_as: int = REQ(json_validator=check_int, default=PreregistrationUser.INVITE_AS["MEMBER"]),
+    invite_as: int = REQ(
+        json_validator=check_int_in(
+            list(PreregistrationUser.INVITE_AS.values()),
+        ),
+        default=PreregistrationUser.INVITE_AS["MEMBER"],
+    ),
     stream_ids: List[int] = REQ(json_validator=check_list(check_int)),
 ) -> HttpResponse:
 
@@ -54,8 +59,6 @@ def invite_users_backend(
         # Guest users case will not be handled here as it will
         # be handled by the decorator above.
         raise JsonableError(_("Insufficient permission"))
-    if invite_as not in PreregistrationUser.INVITE_AS.values():
-        raise JsonableError(_("Must be invited as an valid type of user"))
     check_if_owner_required(invite_as, user_profile)
     if (
         invite_as