api.main: catch 'DuplicateKeyError' exception

Need to catch an exception and return proper
error message when '/user' endpoint receives
a username that has already been taken.

Signed-off-by: Jeny Sadadia <[email protected]>

Author: Jeny Sadadia

api/main.py

@@ -17,6 +17,7 @@
     SecurityScopes
 )
 from bson import ObjectId, errors
+from pymongo.errors import DuplicateKeyError
 from .auth import Authentication, Token
 from .db import Database
 from .models import Node, User, Password
@@ -94,6 +95,11 @@ async def post_user(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail=str(error)
         ) from error
+    except DuplicateKeyError as error:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"{username} is already taken.Try with different username."
+        ) from error
     await pubsub.publish_cloudevent('user', {'op': operation,
                                              'id': str(obj.id)})
     return obj