feat: allow initializing AuthKit with secrets from outside process.env

[ShooTeX]

Problem

AuthKit for Next.js currently requires all secrets (WORKOS_API_KEY, WORKOS_CLIENT_ID, WORKOS_COOKIE_PASSWORD, etc.) to be provided as environment variables. This is limiting for:

• Applications that pull secrets from a secrets manager (AWS Secrets Manager, HashiCorp Vault, Azure Key Vault, GCP Secret Manager, etc.)
• Environments where secrets aren't available in process.env at startup
• Serverless runtimes that inject secrets outside the process environment

Proposed Solution

Export an initAuthKit(config) function that accepts configuration values programmatically. Values set via initAuthKit take precedence over environment variables; missing keys fall back to the corresponding env var. This means existing deployments that rely on env vars work without any changes.

import { initAuthKit } from '@workos-inc/authkit-nextjs';

initAuthKit({
  apiKey: await secrets.get('WORKOS_API_KEY'),
  clientId: await secrets.get('WORKOS_CLIENT_ID'),
  cookiePassword: await secrets.get('WORKOS_COOKIE_PASSWORD'),
  redirectUri: 'https://myapp.com/callback',
});

initAuthKit should be called before any other AuthKit function. Successive calls are merged, so groups of settings can be set independently.