Cross-platform cloud save solution for mobile, console and PC?

I've a multiplatform single-player game and want to offer cloud saves so players can transition from PC to mobile to XBox. I'm seeing lots of sophisticated Cloud services offering everything under the sun but all I want at the moment is this basic, very low overhead service. Are there any solutions out there? I'm thinking of a system where users put in their ID in my game and the save file is sync'd by that, hopefully avoiding the need to use Steam, iOS, Google, Xbox etc. accounts all managed together.