Purpose

Multisite activation endpoint. Validates signup activation keys and completes user/site activation.

Flow

• Defines WP_INSTALLING and loads WordPress + front-end header.
• Requires multisite; otherwise redirects to registration.
• Reads activation key from query/POST/cookie and calls wpmu_activate_signup().
• Sets appropriate HTTP status (404/400) for invalid states.
• Renders activation form or success/error messaging.

Key functions called

• wpmu_activate_signup()
• get_site()
• wp_login_url() / wp_lostpassword_url()
• switch_to_blog() / restore_current_blog() (for site URL/login)

Hooks fired

• Actions:
  • activate_header
  • activate_wp_head