chore: move the go code into a subfolder

apps/api/internal/domain/oidc_code_challenge.go

@@ -0,0 +1,17 @@
+package domain
+
+type OIDCCodeChallenge struct {
+	Challenge string
+	Method    OIDCCodeChallengeMethod
+}
+
+func (c *OIDCCodeChallenge) IsValid() bool {
+	return c.Challenge != ""
+}
+
+type OIDCCodeChallengeMethod int32
+
+const (
+	CodeChallengeMethodPlain OIDCCodeChallengeMethod = iota
+	CodeChallengeMethodS256
+)