Air carrier Captain reported a temporary loss of control during cruise due to moderate to severe turbulence.

Narrative

Constant light to occasional moderate turbulence was encountered for several minutes. Winds were direct crosswind from 270/165 knots. FO had slowed the aircraft for the bumps. All passengers were seated. All flight attendants were in their jump seats. Aircraft suddenly rolled right and went to approximately 35 degrees angle of bank (possibly more; as it was very abrupt). ROLL AUTHORITY was annunciated on the Primary Flight Display and 'bank angle' was heard once. Autopilot did not disconnect; but rolled aircraft back to wings level; again very rapidly. The entire event lasted only a couple of seconds. The aircraft did not overspeed because my FO had already slowed to aircraft prior to this event. Voice reported severe turbulence to ATC; and requested a descent to below the SIGMET reported turbulence area of FL270 to FL370. Rode moderate turbulence all the way to FL250. During the descent; checked on flight attendants and confirmed no one in the cabin was out of their seats and no one was injured. Rest of flight to ZZZ was uneventful.