Calling SingalR\poll?transport=longpolling issue
whenever we change the messageid of the above request we are getting the all the connections history means all the methods are coming as response.please see the attached image for your reference.

That's expected, the messageID is used by the client to tell the server which message it received last. So if you change the messageID to an older ID then you'll get messages since that older ID.
And the concern about auth is not valid because your connection is authenticated via the connectionToken in the query string.
Also, if that's real data you should probably reset the SessionTokens and Login IDs.
cc @halter73
And the concern about auth is not valid because your connection is authenticated via the connectionToken in the query string.
Additionally, if the authenticated user has a non-empty Context.User.Identity.Name that IsAuthenticated when the SignalR connection is established, SignalR will verify every other request with that same connectionToken is authenticated with the same user name or else it will reject the request with a 403.
https://github.com/SignalR/SignalR/blob/d5a2dcb9e09ec97631a4f51b4dc7b75735277ca4/src/Microsoft.AspNet.SignalR.Core/PersistentConnection.cs#L339-L344
That's expected, the messageID is used by the client to tell the server which message it received last. So if you change the messageID to an older ID then you'll get messages since that older ID.
And the concern about auth is not valid because your connection is authenticated via the connectionToken in the query string.
Also, if that's real data you should probably reset the SessionTokens and Login IDs.
cc @halter73
is there any possibility to overcome this issue? please suggest me? if any code changes is needed i will try to do , please help on this?
is there any possibility to overcome this issue?
What issue? You aren't leaking any data because the data has already been sent to this client before.