Fix custom URL for HTTP ip method (fix #203)

pkg/publicip/http/providers.go

@@ -47,6 +47,10 @@ var (
 )
 
 func ValidateProvider(provider Provider, version ipversion.IPVersion) error {
+	if strings.HasPrefix(string(provider), "url:https://") { // custom HTTP url
+		return nil
+	}
+
 	for _, possible := range ListProviders() {
 		if provider == possible {
 			_, ok := provider.url(version)

pkg/publicip/http/providers_test.go

@@ -53,6 +53,10 @@ func Test_ValidateProvider(t *testing.T) {
 			provider: Google,
 			version:  ipversion.IP4or6,
 		},
+		"custom url": {
+			provider: Provider("url:https://ip.com"),
+			version:  ipversion.IP4or6,
+		},
 		"invalid for ip version": {
 			provider: Google,
 			version:  ipversion.IP4,