feat(cert): add registry-based DNS provider system with 21 libdns providers

Refs #37

internal/cert/dnsproviders/huaweicloud.go

@@ -0,0 +1,25 @@
+package dnsproviders
+
+import (
+	"github.com/caddyserver/certmagic"
+	"github.com/libdns/huaweicloud"
+)
+
+func init() {
+	Register(&Provider{
+		Names:   []string{"huaweicloud", "huawei"},
+		EnvVars: []string{"HUAWEICLOUD_ACCESS_KEY_ID", "HUAWEICLOUD_SECRET_ACCESS_KEY", "HUAWEICLOUD_REGION_ID"},
+		Build: func(env map[string]string) (certmagic.DNSProvider, error) {
+			id := firstOf(env, "HUAWEICLOUD_ACCESS_KEY_ID", "HUAWEI_ACCESS_KEY_ID")
+			secret := firstOf(env, "HUAWEICLOUD_SECRET_ACCESS_KEY", "HUAWEI_SECRET_ACCESS_KEY")
+			if id == "" || secret == "" {
+				return nil, missingEnvErr("huaweicloud", "HUAWEICLOUD_ACCESS_KEY_ID", "HUAWEICLOUD_SECRET_ACCESS_KEY")
+			}
+			return &huaweicloud.Provider{
+				AccessKeyId:     id,
+				SecretAccessKey: secret,
+				RegionId:        firstOf(env, "HUAWEICLOUD_REGION_ID", "HUAWEI_REGION"),
+			}, nil
+		},
+	})
+}