os-ddclient: opnsense backend and cloudflare: use API token if available

[juantxorena]

If the username is "token", use the password as an API token instead of a global one. Tested locally. This should fix bug #3427.

I'm not a python programmer, please feel free to fix the style.

[AdSchellevis]

I think this is a bit too obscure, maybe we better switch on username provided or not (no username equals Bearer).
Can I interest you to contribute to the documentation as well ? (https://github.com/opnsense/docs/blob/master/source/manual/dynamic_dns.rst#L6) I would be good to describe the different options for cloudflare.

[juantxorena]

I just copied the same logic as ddclient, so the exact same config would work when changing backends. I would agree with the empty name. Maybe we can check for both empty and "token"? It wouldn't be compatible with ddclient, though.

About the documentation, maybe I can have a look at the weekend. Would there be a specific documentation for cloudflare?

[AdSchellevis]

that's a good point, when it's clear from the documentation, it shouldn't be an issue to support "token" as well or maybe a simple check if it's an email address (if I understand this correctly, only email addresses are supported for X-auth-* headers)

[juantxorena]

I created a PR for the docs: opnsense/docs#469

I'm very bad at writing documentation, please feel free to rewrite the whole thing. I think it's better to leave the code as it is, for ddclient compatibility, and also because checking if the username is an email is harder (it's just a regex, but just checking for "token" is easier). If I have to change this, please let me know.

[AdSchellevis]

merged with minor modifications in 02f273f