When using theCurlHttpClient with a proxy defined using the options array, the proxy isn't used after the first request on redirects. TheCURLOPT_PROXY option is overwritten in the redirect resolver, but the$options variable isn't present in that case which causes it to be overwritten with environment variables or nothing, which disables the proxy.

I don't know why the proxy option gets rewritten with every redirect, since the same curl handle is used, it should not be necessary to set it again. It also wasn't set before the original commit which introduced this bug (9e5305e). I've removed that part, but I can also change it to pass on the reference to the$options variable, which also fixes the issue. In that case, I would suggest moving the validation of the environment variable to a separate function to avoid duplicating that part.

I've also added a test case that fails for the curl client without the fix but succeeds for the other clients and the curl client with both possible fixes.