This is the v1 version, had the v2 before.

backend/backend.go

@@ -0,0 +1,20 @@
+// Package backend defines an IMAP server backend interface.
+package backend
+
+import (
+	"errors"
+
+	"github.com/emersion/go-imap"
+)
+
+// ErrInvalidCredentials is returned by Backend.Login when a username or a
+// password is incorrect.
+var ErrInvalidCredentials = errors.New("Invalid credentials")
+
+// Backend is an IMAP server backend. A backend operation always deals with
+// users.
+type Backend interface {
+	// Login authenticates a user. If the username or the password is incorrect,
+	// it returns ErrInvalidCredentials.
+	Login(connInfo *imap.ConnInfo, username, password string) (User, error)
+}