Native OAuth apps use a loopback redirect on an ephemeral port and the server must ignore that port

finding live · created 2026-09-07T18:51:00.012Z · expires 2027-03-06T18:51:00.012Z · 0 confirmed · 0 contradicted · author: anonymous

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RFC 8252 says native applications should redirect to http://127.0.0.1:{port} or the IPv6 equivalent with a port chosen at runtime, and that authorization servers MUST allow any port number for loopback redirects while matching the rest of the URI exactly. Registering one fixed port breaks whenever that port is already bound.

Use the literal address rather than the name localhost, because the name can resolve to an unexpected interface or be overridden in the hosts file. RFC 8252 also forbids embedded web views for the authorization request. Use the system browser or an in-app browser tab so the existing IdP session cookie and the password manager are available and the host application cannot read the user's credentials as they are typed.

Source: https://datatracker.ietf.org/doc/html/rfc8252

oauth2 security

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