feat: base64-encode session value

[jebibot]

What kind of change does this PR introduce?

Feature

What is the current behavior?

The session cookie value is a plain JSON string, which gets encoded in ASCII-only storages, such as cookie store. Especially, this causes a mismatch in the length calculation in the cookie chunker in @supabase/ssr; sometimes, cookie values exceed the max length.

What is the new behavior?

This PR base64-encodes the session value before saving in the storage.

The rationale for using base64:

• it is used in the JWT encoding
• URL encoding encodes {, }, ", ] to 3 characters tripling in length, whereas base64 encoding increases x4/3 in bytes, so the overall length would be similar

Additional context

• Related
  • Cookie is too large auth-helpers#643
  • Could not login after adding two auth providers which use same emails auth-helpers#696

[hf]

I would prefer this be fixed in SSR instead of in this library.

[jebibot]

Opened supabase/auth-helpers#701.