B737 Captain reported after landing and while taxing losing control of the steering system resulting in switching to alternate system and taxing to the gate.

Narrative

Upon a normal landing performed by the First Officer (pilot flying (PF)) on Runway XXL in ZZZ and after a positive exchange of controls; I taxied out on Taxiway 1 to join Taxiway 2 and make a 90 degree turn to join Taxiway 3. Upon making the 90 degree left turn to join 3; the caution light 'FLT Control' came out and simultaneously I lost control of the steering system. I brought the airplane to a complete stop and after further review of the overhead panel; we realized we had a total lost of HYD A system. We ran the appropriate QRH and the items applicable to this event. once we accomplished all items; we contacted ZZZ Maintenance; as well as the Cabin Crew to informed them of the event and that after reconfigured the steering system to the alternate system; we were able to taxi to the gate. with their concurrence; we continue a two engine taxi to the gate XX. Upon reaching the gate; Maintenance took over the airplane. Maintenance confirmed a total rupture of a HYD Spoiler line thus leaking all fluid. All procedures were conducted in accordance with the Flight Manual (FM) and FOM.