Use in-memory FS or buffer instead of /tmp WorkDir

[VojtechVitek]

https://github.com/goware/saml/blob/master/files.go#L11

https://github.com/spf13/afero
https://github.com/blang/vfs
or byte buffer
or similar..

[VojtechVitek]

I see, the xmlsec1 actually picks up the certs from the FileSystem..

Hmm.. what can we do to avoid writing into the disk?

[xiam]

Yeah, this is because we need xmlsec1 to read certain things from disk. In order to not write things to disk an user can mount a small RAM filesystem, such as tmpfs.

[VojtechVitek]

@xiam I'm really hoping we could replace xmlsec1 binary with a pure Go package one day.