added oauth flow to get authorization code

pkg/oauth/cookies.go

@@ -0,0 +1,45 @@
+package oauth
+
+import (
+	"encoding/base64"
+	"net/http"
+
+	"github.com/pkg/errors"
+)
+
+func SetStateCookie(w http.ResponseWriter, uak []byte, ssl bool) {
+	encodedUak := base64.RawURLEncoding.EncodeToString(uak)
+	http.SetCookie(w, &http.Cookie{
+		Name:     "oauth_uak",
+		Value:    encodedUak,
+		Path:     "/",
+		MaxAge:   300,
+		HttpOnly: true,
+		Secure:   ssl,
+		SameSite: http.SameSiteLaxMode,
+	})
+}
+
+func GetStateCookie(r *http.Request) ([]byte, error) {
+	if r == nil {
+		return nil, errors.New("Request cannot be nil")
+	}
+	cookie, err := r.Cookie("oauth_uak")
+	if err != nil {
+		return nil, err
+	}
+	uak, err := base64.RawURLEncoding.DecodeString(cookie.Value)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to decode userAgentKey from cookie")
+	}
+	return uak, nil
+}
+
+func DeleteStateCookie(w http.ResponseWriter) {
+	http.SetCookie(w, &http.Cookie{
+		Name:   "oauth_uak",
+		Value:  "",
+		Path:   "/",
+		MaxAge: -1,
+	})
+}