[FEATURE] Support for state in login_link in Auth0 OAuth client

[akashkroy]

Description

Currently, the login_link method in the Auth0AppClient (and possibly other OAuth clients) does not support passing a custom state parameter. The state parameter is important for maintaining state between the authentication request and callback, and is a recommended security best practice to prevent CSRF attacks.

Expected Behavior

• The login_link method should accept an optional state argument.
• If provided, the state value should be included in the generated Auth0 authorization URL as a query parameter.

Current Behavior

• The state parameter is not supported or ignored in the current implementation of login_link for Auth0AppClient.

Example

client = Auth0AppClient(...)
auth_url = client.login_link(req, state='my-custom-state')
# The generated URL should include: ...&state=my-custom-state

Motivation

Supporting the state parameter is important for:

• Security (CSRF protection)
• Passing application-specific context through the OAuth flow

Additional Context

• Auth0 Docs: State Parameter
• This feature would bring the Auth0 client in line with OAuth2 best practices and other client implementations.