An identity gateway is a service or interface that sits between users and the systems they want to access, mediating login, account linking, and session creation. In practice, it may handle sign-in redirects, token exchange, single sign-on, or account selection. In the browser context, it can make the browser a front door for identity rather than just a place to view pages.
This matters in cyber security because the gateway becomes a high-value trust point: if it is abused, attackers can steal credentials, hijack sessions, or trick users into approving access they did not intend. Defenders use identity gateways to enforce multi-factor authentication, validate tokens, apply policy checks, and reduce exposure of internal applications. In attacks, fake login pages, consent phishing, and weak session handling are common ways to target this layer.