VPN Unlimited support (#499)

- Fixes #420 
- Revert to docker/build-push-action@v2.4.0

internal/provider/vpnunlimited/openvpnconf.go

@@ -0,0 +1,69 @@
+package vpnunlimited
+
+import (
+	"strconv"
+
+	"github.com/qdm12/gluetun/internal/configuration"
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
+	"github.com/qdm12/gluetun/internal/provider/utils"
+)
+
+func (p *Provider) BuildConf(connection models.OpenVPNConnection,
+	username string, settings configuration.OpenVPN) (lines []string) {
+	lines = []string{
+		"client",
+		"dev tun",
+		"nobind",
+		"persist-key",
+		"tls-exit",
+		"remote-cert-tls server",
+
+		// VPNUnlimited specific
+		"reneg-sec 0",
+		"ping 5",
+		"ping-exit 30",
+		"comp-lzo no",
+		"route-metric 1",
+
+		// Added constant values
+		"auth-nocache",
+		"mute-replay-warnings",
+		"pull-filter ignore \"auth-token\"", // prevent auth failed loops
+		"auth-retry nointeract",
+		"suppress-timestamps",
+
+		// Modified variables
+		"verb " + strconv.Itoa(settings.Verbosity),
+		// "auth-user-pass " + constants.OpenVPNAuthConf,
+		connection.ProtoLine(),
+		connection.RemoteLine(),
+	}
+
+	if settings.Cipher != "" {
+		lines = append(lines, utils.CipherLines(settings.Cipher, settings.Version)...)
+	}
+
+	if settings.Auth != "" {
+		lines = append(lines, "auth "+settings.Auth)
+	}
+
+	if settings.MSSFix > 0 {
+		lines = append(lines, "mssfix "+strconv.Itoa(int(settings.MSSFix)))
+	}
+
+	if !settings.Root {
+		lines = append(lines, "user "+username)
+	}
+
+	lines = append(lines, utils.WrapOpenvpnCA(
+		constants.VPNUnlimitedCertificateAuthority)...)
+	lines = append(lines, utils.WrapOpenvpnCert(
+		settings.Provider.ExtraConfigOptions.ClientCertificate)...)
+	lines = append(lines, utils.WrapOpenvpnKey(
+		settings.Provider.ExtraConfigOptions.ClientKey)...)
+
+	lines = append(lines, "")
+
+	return lines
+}