Add different authentication modes to JS SDK

[kschiffer]

Summary

Since #2564, we allow authorization by session cookie. The SDK does however not support this new authentication mode. This should be added.

Why do we need this?

To use the JS SDK with a session cookie for authentication, e.g. for the account app (#1422).

What is already there? What do you see now?

• SDK support for authentication via Bearer token (API Key or access token)
• The stack supporting authentication using a session cookie

What is missing? What do you want to see?

Possibility to configure the SDK to use the session cookie (in conjunction with a CSRF token) for authentication.

How do you propose to implement this?

Currently, the constructor signature for the SDK client class is TtnLw(token, options)

1. The class name should be updated to TTS()
2. We should use the options object pattern and use a single argument for the constructor:

// For key authentication
const ttsClient = new TTS({
  authentication: {
    mode: 'token',
    key: token,
  },
  stackConfig: config,
  …
})

// For session authentication
const ttsClient = new TTS({
  authentication: {
    mode: 'session',
    csrfToken: csrf,
  },
  stackConfig: config,
  …
})

How do you propose to test this?

Update unit tests and manual testing. Any issue here should also be caught by our e2e's.

Can you do this yourself and submit a Pull Request?

Yes.