More porting from rep (#2388)

* More porting from rep

* Address review feedback

builtin/logical/mssql/backend.go

@@ -32,6 +32,8 @@ func Backend() *backend {
 			secretCreds(&b),
 		},
 
+		Invalidate: b.invalidate,
+
 		Clean: b.ResetDB,
 	}
 
@@ -112,6 +114,13 @@ func (b *backend) ResetDB() {
 	b.db = nil
 }
 
+func (b *backend) invalidate(key string) {
+	switch key {
+	case "config/connection":
+		b.ResetDB()
+	}
+}
+
 // LeaseConfig returns the lease configuration
 func (b *backend) LeaseConfig(s logical.Storage) (*configLease, error) {
 	entry, err := s.Get("config/lease")