Refactor auth: add token and store implementations (#1230)

* Refactor auth: add token and memory implementations

* Fix typo

* Remove memory auth (implemented already by the store implementation), revert default to noop

* Add grpc header

* Global Config

* config/global => util/config

* Rename package to remove confict

* Tweak

* Improve Error Handling

util/config/config.go

@@ -0,0 +1,88 @@
+package config
+
+import (
+	"io/ioutil"
+	"os"
+	"os/user"
+	"path/filepath"
+
+	conf "github.com/micro/go-micro/v2/config"
+	"github.com/micro/go-micro/v2/config/source/file"
+)
+
+// FileName for global micro config
+const FileName = ".micro"
+
+// Get a value from the .micro file
+func Get(key string) (string, error) {
+	// get the filepath
+	fp, err := filePath()
+	if err != nil {
+		return "", err
+	}
+
+	// create a new config
+	c, err := conf.NewConfig(
+		conf.WithSource(
+			file.NewSource(
+				file.WithPath(fp),
+			),
+		),
+	)
+	if err != nil {
+		return "", err
+	}
+
+	// load the config
+	if err := c.Load(); err != nil {
+		return "", err
+	}
+
+	// set a value
+	return c.Get(key).String(""), nil
+}
+
+// Set a value in the .micro file
+func Set(key, value string) error {
+	// get the filepath
+	fp, err := filePath()
+	if err != nil {
+		return err
+	}
+
+	// write the file if it does not exist
+	if _, err := os.Stat(fp); os.IsNotExist(err) {
+		ioutil.WriteFile(fp, []byte{}, 0644)
+	}
+
+	// create a new config
+	c, err := conf.NewConfig(
+		conf.WithSource(
+			file.NewSource(
+				file.WithPath(fp),
+			),
+		),
+	)
+	if err != nil {
+		return err
+	}
+
+	// load the config
+	if err := c.Load(); err != nil {
+		return err
+	}
+
+	// set a value
+	c.Set(value, key)
+
+	// write the file
+	return ioutil.WriteFile(fp, c.Bytes(), 0644)
+}
+
+func filePath() (string, error) {
+	usr, err := user.Current()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(usr.HomeDir, FileName), nil
+}