We have a Sitecore 9.0.1 solution where the login times have been increasing slowly and is now sometimes up to 40 seconds. After doing some research I came to the conclusion that it was a known 9.0.1/9.0.2 bug which causes properties from login tickets to not get cleaned out from the core database.
As we are on the verge of upgrading that Sitecore solution I didn't find it necessary to install the bugfix, I was however going to do some cleanup in the Core database.
I came up with the following SQL script which I ran a couple of times and changed the year value, from 2017 to 2020.
DELETE FROM [dbo].[Properties] WHERE [dbo].[Properties].[Key] like '%SC_TICKET%' AND [dbo].[Properties].[Value] like '%^2019%';
In the end I removed 25 000 lines from the Properties table and the login to Sitecore is now fast again.