Support PSR HttpClient

[SamMousa]

Would you consider adding support for (or switching to) PSR-18 HTTP Clients?

We force all our outbound traffic through an egress proxy and therefore prefer to be in control of all (HTTP) clients / calls.

[skoerfgen]

Yes, that sounds like a great enhancement. I just put together a prototype with support for PSR-18 HTTP Clients.

There is now a new method "setHTTPHandler" with two arguments:

1. Psr\Http\Client\ClientInterface
2. Psr\Http\Message\RequestFactoryInterface

For example:

$ac=new ACMECert();
$client=new \GuzzleHttp\Client();
$factory=new \GuzzleHttp\Psr7\HttpFactory();
$ac->setHTTPHandler($client,$factory);

Here is a working example: https://github.com/skoerfgen/ACMECert/actions/runs/35739811874/job/106786324141

The code is in the psr branch: https://github.com/skoerfgen/ACMECert/tree/psr