An Azure relational database service.
For what it's worth, when I run DBCC TRACESTATUS in my Azure SQL Database, there are no less than 31 trace flags turned on, including 8017. I may recognise a few of them, but far from all. I would assume that they are set by the service and they should not be a concern to you.
The trace flag may be undocumented and unsupported for the box product, but it is a different thing you get the database as a service. Then Microsoft is setting this flag for you, which means that by definition it is supported.
As for information for what 8017 does, see Paul White's answer on this thread on Stack Exchange: https://dba.stackexchange.com/questions/48580/trace-flag-and-which-need-to-be-turned-off-and-why