Most of the GraphQL documentation can be found inside the FreePBX App. You can find out more about the GraphQL support in FreePBX here: GraphQL support in FreePBX 15 | FreePBX - Let Freedom Ring
Unfortunately, I don’t think there is a way to update the extensions’s user name. The GraphQL library is only about 20% complete and the rest library is in the same state it seems. The userman module, where the users live, don’t look to have a GraphQL API. It DOES have a Rest API, but it looks to be read only.
The semi-good news is that device mutation look to be supported by the GraphQL library. I did pull up the code where the device is updated, but it looks like it just removes the device and creates a new one: https://git.freepbx.org/projects/FREEPBX/repos/core/browse/Api/Gql/Devices.php?at=refs%2Fheads%2Frelease%2F15.0#61-62
I will note that a device and a user in FreePBX are two different objects.
Some of the queries I played around with were:
And the Update query, but it looks to have a bug in it:
