Custom UID and GID for subprocesses and files written (#116) Fix #116

- Environment variables `UID` and `GID`, both defaulting to `1000`
- All subprocesses (openvpn, tinyproxy, etc.) run using the UID and GID given
- All files are written with an ownership for the UID and GID given
- Port forwarded file has also ownership for UID, GID and read permission only

internal/params/ids.go

@@ -0,0 +1,15 @@
+package params
+
+import (
+	libparams "github.com/qdm12/golibs/params"
+)
+
+// GetUID obtains the user ID to use from the environment variable UID
+func (p *paramsReader) GetUID() (uid int, err error) {
+	return p.envParams.GetEnvIntRange("UID", 0, 65535, libparams.Default("1000"))
+}
+
+// GetGID obtains the group ID to use from the environment variable GID
+func (p *paramsReader) GetGID() (gid int, err error) {
+	return p.envParams.GetEnvIntRange("GID", 0, 65535, libparams.Default("1000"))
+}