https://github.com/acmesh-official/acme.sh#supported-ca
But it seems that acme.sh got bought by zero ssl, which would explain that it's their default now..
Out of honest interest, where did they fail to honor "7.3.1 Finding an Account URL Given a Key"?
Well... it doesn't work. Let me quote the RFC:
> If the server receives a newAccount request signed with a key for which it already has an account registered with the provided account key, then it MUST return a response with status code 200 (OK) and provide the URL of that account in the Location header field.
With ZeroSSL you could only call `newAccount` once; any subsequent call will fail, while according to the RFC it should return the URL of the account. So you have to either a) use their proprietary API to recover the URL (I sent them a bug report for this and that's what they basically told me), or b) save the URL along with the account key (which you don't have to do for any other ACME provider).
> ZeroSSL.com
I kinda wish people would stop recommending them. This might have changed, but last time I tried ZeroSSL (~a year ago) it was not RFC 8555 compliant (specifically section 7.3.1), and you were basically supposed to use their own proprietary API to deal with the issue. So you can't always switch transparently.
If you need an alternative use Buypass. Also free, and they're actually RFC 8555 compliant.