doveauth: add invite_token to override nocreate file

[missytake]

fix #594

To try it out: dcaccount:https://c17.testrun.org/new?asdf
(Right now broken client-side because of chatmail/core#6988)

[missytake]

Hm -.-

right now, when I run curl -X POST https://c17.testrun.org/new?asdf, it responds with a passphrase that contains asdf.

but when I copy the very same URL into Delta Chat's "create new profile > use other server > scan invitation code", it tries to login with a passphrase which doesn't contain asdf. It seems the ?asdf parameter is stripped when Delta Chat sends a POST request?
When I login manually with a passphrase that contains asdf it works.

[missytake]

So server-side everything works, just client-side it doesn't.

[missytake]

So server-side everything works, just client-side it doesn't.

With 2.x.x it works :) So we can merge this now.

[dillfrescott]

Awesome, can't wait for the merge! Good job!