serve http: support unix sockets and multiple listners

- add support for unix sockets (which skip the auth).
- add support for multiple listeners
- collapse unnecessary internal structure of lib/http so it can all be
  imported together
- moves files in sub directories of lib/http into the main lib/http
  directory and reworks the code that uses them.

See: https://forum.rclone.org/t/wip-rc-rcd-over-unix-socket/33619
Fixes: #6605

lib/http/auth.go

@@ -0,0 +1,70 @@
+package http
+
+import (
+	"github.com/rclone/rclone/fs/config/flags"
+	"github.com/spf13/pflag"
+)
+
+// Help contains text describing the http authentication to add to the command
+// help.
+var AuthHelp = `
+#### Authentication
+
+By default this will serve files without needing a login.
+
+You can either use an htpasswd file which can take lots of users, or
+set a single username and password with the ` + "`--user` and `--pass`" + ` flags.
+
+Use ` + "`--htpasswd /path/to/htpasswd`" + ` to provide an htpasswd file.  This is
+in standard apache format and supports MD5, SHA1 and BCrypt for basic
+authentication.  Bcrypt is recommended.
+
+To create an htpasswd file:
+
+    touch htpasswd
+    htpasswd -B htpasswd user
+    htpasswd -B htpasswd anotherUser
+
+The password file can be updated while rclone is running.
+
+Use ` + "`--realm`" + ` to set the authentication realm.
+
+Use ` + "`--salt`" + ` to change the password hashing salt from the default.
+`
+
+// CustomAuthFn if used will be used to authenticate user, pass. If an error
+// is returned then the user is not authenticated.
+//
+// If a non nil value is returned then it is added to the context under the key
+type CustomAuthFn func(user, pass string) (value interface{}, err error)
+
+// AuthConfig contains options for the http authentication
+type AuthConfig struct {
+	HtPasswd     string       // htpasswd file - if not provided no authentication is done
+	Realm        string       // realm for authentication
+	BasicUser    string       // single username for basic auth if not using Htpasswd
+	BasicPass    string       // password for BasicUser
+	Salt         string       // password hashing salt
+	CustomAuthFn CustomAuthFn `json:"-"` // custom Auth (not set by command line flags)
+}
+
+// AddFlagsPrefix adds flags to the flag set for AuthConfig
+func (cfg *AuthConfig) AddFlagsPrefix(flagSet *pflag.FlagSet, prefix string) {
+	flags.StringVarP(flagSet, &cfg.HtPasswd, prefix+"htpasswd", "", cfg.HtPasswd, "A htpasswd file - if not provided no authentication is done")
+	flags.StringVarP(flagSet, &cfg.Realm, prefix+"realm", "", cfg.Realm, "Realm for authentication")
+	flags.StringVarP(flagSet, &cfg.BasicUser, prefix+"user", "", cfg.BasicUser, "User name for authentication")
+	flags.StringVarP(flagSet, &cfg.BasicPass, prefix+"pass", "", cfg.BasicPass, "Password for authentication")
+	flags.StringVarP(flagSet, &cfg.Salt, prefix+"salt", "", cfg.Salt, "Password hashing salt")
+}
+
+// AddAuthFlagsPrefix adds flags to the flag set for AuthConfig
+func AddAuthFlagsPrefix(flagSet *pflag.FlagSet, prefix string, cfg *AuthConfig) {
+	cfg.AddFlagsPrefix(flagSet, prefix)
+}
+
+// DefaultAuthCfg returns a new config which can be customized by command line flags
+func DefaultAuthCfg() AuthConfig {
+	return AuthConfig{
+		Salt: "dlPL2MqE",
+	}
+}