ldap: Use new helper for checking realm status.

We intentionally don't fix the indentation that now feels ridiculous
below in order to make it easier to see what's actually changing in
this commit.

zproject/backends.py

@@ -452,14 +452,9 @@ class ZulipLDAPAuthBackend(ZulipLDAPAuthBackendBase):
 
         try:
             username = self.django_to_ldap_username(username)
-            user_profile = ZulipLDAPAuthBackendBase.authenticate(self,
-                                                                 username=username,
-                                                                 password=password)
-            if user_profile is None:
-                return None
-            if not user_matches_subdomain(realm.subdomain, user_profile):
-                return None
-            return user_profile
+            return ZulipLDAPAuthBackendBase.authenticate(self,
+                                                         username=username,
+                                                         password=password)
         except ZulipLDAPException:
             return None  # nocoverage # TODO: this may no longer be possible
 
@@ -474,12 +469,23 @@ class ZulipLDAPAuthBackend(ZulipLDAPAuthBackendBase):
 
             username = ldap_user.attrs[settings.LDAP_EMAIL_ATTR][0]
 
-        try:
-            user_profile = get_user_profile_by_email(username)
-            if not user_profile.is_active or user_profile.realm.deactivated:
-                raise ZulipLDAPException("Realm has been deactivated")
+        return_data = {}  # type: Dict[str, Any]
+        user_profile = common_get_active_user(username, self._realm, return_data)
+        if return_data.get("inactive_realm"):
+            raise ZulipLDAPException("Realm has been deactivated")
+        if return_data.get("inactive_user"):
+            # Bug: This isn't the correct response, but it's what the old code did.
+            raise ZulipLDAPException("Realm has been deactivated")
+        if return_data.get("invalid_subdomain"):
+            # TODO: Implement something in the caller for this to
+            # provide a nice user-facing error message for this
+            # situation (right now it just acts like any other auth
+            # failure).
+            raise ZulipLDAPException("Wrong subdomain")
+        if user_profile is not None:
             return user_profile, False
-        except UserProfile.DoesNotExist:
+
+        if user_profile is None:
             if self._realm is None:
                 raise ZulipLDAPConfigurationError("Realm is None", self.REALM_IS_NONE_ERROR)
             # No need to check for an inactive user since they don't exist yet