Depending on the org's settings, all users logging into Core (including users making API requests through an API key) are subject to the following rules:
If IP authorization is off, users can log in without IP validation.
If IP authorization is on, users' IP addresses are validated against the org's IP allow list. This applies to both SSO and basic access authentication requests (i.e., usernames and passwords).
IP token validation must be enabled separately from IP authorization.
If IP authorization is set to bypass_sso, SSO users can log in without IP validation, but basic access authentication requests are validated against the IP allow list.
Multi-Tenancy (Multiple Orgs)
If a user is a member of multiple orgs but does not have access to an org because their IP address wasn't validated against the allow list, that org will not display after successful login. If no orgs are accessible under IP authorization control, an Access Denied error is displayed after login.
If enabled on the org, admins can enable IP authorization control on individual Anonymous Login URLs. If the user's IP address doesn't match an entry in the list, a 403 error is displayed. This is captured in the User Audit Trail as an Unsuccessful Anonymous Login event.