microsoftonline: gzip of cookie no longer enough

[mediumdaver]

I am getting the infamous "securecookie: the value is too long" error when using Microsoft online provider. It seems that the returned data, even after gzip compression, is coming in at around 3,974 bytes and failing to be set.

We need a new mechanism, perhaps using web storage or splitting the cookie into parts?

[dobin]

I have the same issue when using azureadv2 authentication provider.

Edit: I also dont use the goth cookies. I disabled it like this, but maybe there's a better solution:

	store := sessions.NewFilesystemStore("", []byte("fsstore"))
	gothic.Store = store

[joriszwart]

@dobin: see my comment in #463 (comment) for a possible solution increasing the maximum size.