Unlike portal::Keyring, we currently have no (direct) way to change the password of a dbus::Collection. I think the main problem here is that changing a collection password isn't part of the secret-service dbus specification.

Seahorse / gnome keyring work around this and have something custom implemented (org.gnome.keyring.InternalUnsupportedGuiltRiddenInterface).

A possible workaround I can see at the moment would be to load the collection as a keyring file via portal::Keyring and change the password there - although I'm not sure how many side effects it would have to fiddle with the keyring file directly instead of using the intended oo7/secret-service api.

I wonder if this is something we can fix on oo7 side, or if we need an updated/extended secret-service dbus specification.