Support Bearer tokens

[n-g]

While at it:

• ensure absolute names are indeed absolute
• fix error handling

Fixes #10

[ofauchon]

Yes,

@n-g : I'd like to to test your PR with caddy webserver, but I can't solve this error.
Any idea how to go further ?

$ go version
go version go1.21.3 linux/amd64

 $ ~/go/bin/xcaddy build v2.7.5 --with github.com/n-g/libdns-gandi
...
2023/10/16 21:07:33 [INFO] exec (timeout=0s): /usr/bin/go get -d -v github.com/n-g/libdns-gandi github.com/caddyserver/caddy/v2@v2.7.5 
go: github.com/n-g/libdns-gandi@v0.0.0-20231012081002-090df437d112 found: parsing go.mod:
	module declares its path as: github.com/libdns/gandi
	        but was required as: github.com/n-g/libdns-gandi
go: github.com/n-g/libdns-gandi@upgrade (v0.0.0-20231012081002-090df437d112) requires github.com/n-g/libdns-gandi@v0.0.0-20231012081002-090df437d112: parsing go.mod:
	module declares its path as: github.com/libdns/gandi
	        but was required as: github.com/n-g/libdns-gandi
...

[n-g]

Yes,

@n-g : I'd like to to test your PR with caddy webserver, but I can't solve this error. Any idea how to go further ?

$ go version
go version go1.21.3 linux/amd64

 $ ~/go/bin/xcaddy build v2.7.5 --with github.com/n-g/libdns-gandi
...
2023/10/16 21:07:33 [INFO] exec (timeout=0s): /usr/bin/go get -d -v github.com/n-g/libdns-gandi github.com/caddyserver/caddy/v2@v2.7.5 
go: github.com/n-g/libdns-gandi@v0.0.0-20231012081002-090df437d112 found: parsing go.mod:
	module declares its path as: github.com/libdns/gandi
	        but was required as: github.com/n-g/libdns-gandi
go: github.com/n-g/libdns-gandi@upgrade (v0.0.0-20231012081002-090df437d112) requires github.com/n-g/libdns-gandi@v0.0.0-20231012081002-090df437d112: parsing go.mod:
	module declares its path as: github.com/libdns/gandi
	        but was required as: github.com/n-g/libdns-gandi
...

Right, I didn't change the go.mod to make the PR clean.

The best way to test this change is to check out github.com/n-g/libdns-gandi and then run
xcaddy build v2.7.5 --with github.com/libdns/gandi=. from that dir.

[obynio]

Alright, just released recently the fix for the legacy certbot plugin, will work on this one asap.