Supabase's Management API at https://api.supabase.com/v1 manages your projects and organizations. (Each project's own data API lives at its own URL instead.)
Get a personal access token at supabase.com. Send it as Authorization: Bearer <token>. In the examples it's written {{SUPABASE_ACCESS_TOKEN}}.
Full reference: https://supabase.com/docs/reference/api/introduction
curl https://api.supabase.com/v1/projects \
-H "Authorization: Bearer {{SUPABASE_ACCESS_TOKEN}}"
curl https://api.supabase.com/v1/organizations \
-H "Authorization: Bearer {{SUPABASE_ACCESS_TOKEN}}"
ref is the project's id from the projects call.
curl https://api.supabase.com/v1/projects/{{PROJECT_REF}}/api-keys \
-H "Authorization: Bearer {{SUPABASE_ACCESS_TOKEN}}"