The same-origin policy is a core browser security rule that stops a script loaded from one website from freely accessing data on another website. Two pages share an origin only when they match on protocol, domain, and port.
When a script tries to read data from a different origin, such as another domain, the browser blocks the response by default. This applies to actions like reading cookies, reading local storage, or reading the content of another site loaded in an iframe. The rule prevents a malicious page from secretly pulling private data from a site where the user is logged in. Exceptions exist through mechanisms like CORS, which let a server explicitly opt in to sharing data with specific outside origins.
Match the strength of this control to what is actually at risk in the workflow.
USER-country-de-session-task01The credential string is the only configuration needed -- "country-de" sets the exit, "session-task01" keeps it consistent, and same-origin policy is handled by the gateway rather than your application code.
Test the setup with a leak-test tool or packet capture to confirm this protection is actually working, not just configured.
Pair this with sane session handling and header hygiene -- no single control covers a full workflow on its own.
Apply the strongest version of this control to logins, payments, and personal data -- it is overkill for public information.
Do not let two workflows that need to stay separate for privacy or account reasons share the same session or IP.
A malicious ad on one site cannot read an email inbox open in another browser tab because the two pages have different origins.
This policy is one of the most important protections that keep logged-in accounts safe while browsing other sites. Understanding it helps explain why some cross-domain requests fail without special server permissions.
Any difference in protocol, such as http versus https, domain, or port creates a different origin, even if the rest of the URL looks the same. All three parts must match exactly for two pages to share an origin.
Sites use CORS headers to explicitly allow certain outside domains to access their resources. The browser then checks these headers and permits the exchange.
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