feat(auth): implement user and device authentication

backend-api/internal/usecase/auth_runtime.go

@@ -0,0 +1,20 @@
+package usecase
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"io"
+)
+
+const opaqueTokenBytes = 32
+
+type CryptoTokenGenerator struct{}
+
+func (CryptoTokenGenerator) NewToken() (string, error) {
+	value := make([]byte, opaqueTokenBytes)
+	if _, err := io.ReadFull(rand.Reader, value); err != nil {
+		return "", errors.New("generate opaque token")
+	}
+	return base64.RawURLEncoding.EncodeToString(value), nil
+}