Explain to the user that their project is inaccessible

services/git-bridge/src/main/java/uk/ac/ic/wlgitbridge/server/Oauth2Filter.java

@@ -78,8 +78,7 @@ public class Oauth2Filter implements Filter {
             );
             return;
         } catch (DisabledRepositoryException e) {
-            Log.info("[{}] Git access disabled", project);
-            throw new ServletException(e);
+            disabled(project, (HttpServletResponse) servletResponse);
         }
         Log.info("[{}] Auth not needed", project);
         filterChain.doFilter(servletRequest, servletResponse);
@@ -204,4 +203,22 @@ public class Oauth2Filter implements Filter {
         w.close();
     }
 
+    private void disabled(
+            String projectName,
+            HttpServletResponse response
+    ) throws IOException {
+        Log.info("[{}] Git access to project disabled.", projectName);
+
+        response.setContentType("text/plain");
+
+        // git special-cases 404 to give "repository '%s' not found",
+        // rather than displaying the raw status code.
+        response.setStatus(404);
+
+        PrintWriter w = response.getWriter();
+        w.println("This project is not accessible over Git.");
+        w.println();
+        w.println("If you think this is an error, contact support at support@overleaf.com.");
+        w.close();
+    }
 }