Add authentication function

Signed-off-by: Asai Neko <sugar@sne.moe>

pkgs/magiclink/magiclink.go

@@ -0,0 +1,51 @@
+package magiclink
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"sync"
+	"time"
+)
+
+type Token struct {
+	Email     string
+	ExpiresAt time.Time
+}
+
+var (
+	store = sync.Map{}
+)
+
+// Generate magic token
+func NewMagicToken(email string, ttl time.Duration) (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+
+	token := base64.RawURLEncoding.EncodeToString(b)
+
+	store.Store(token, Token{
+		Email:     email,
+		ExpiresAt: time.Now().Add(ttl),
+	})
+
+	return token, nil
+}
+
+// Verify magic token
+func VerifyMagicToken(token string) (string, bool) {
+	val, ok := store.Load(token)
+	if !ok {
+		return "", false
+	}
+
+	t := val.(Token)
+	if time.Now().After(t.ExpiresAt) {
+		store.Delete(token)
+		return "", false
+	}
+
+	store.Delete(token)
+	return t.Email, true
+}