CORS

CORS (Cross-Origin Resource Sharing) is a system, consisting of transmitting HTTP headers, that determines whether to block or fulfill requests for restricted resources on a web page from another domain outside the domain from which the resource originated.

The same-origin security policy forbids "cross-domain" requests by default, CORS gives web servers cross-domain access controls, which enable secure cross-domain data transfers.

Learn more

General knowledge

• HTTP access control (CORS) on MDN
• Cross-origin resource sharing on Wikipedia

CORS headers

Access-Control-Allow-Origin

Indicates whether the response can be shared.

Access-Control-Allow-Credentials

Indicates whether or not the response to the request can be exposed when the credentials flag is true.

Access-Control-Allow-Headers

Used in response to a preflight request to indicate which HTTP headers can be used when making the actual request.

Access-Control-Allow-Methods

Specifies the method or methods allowed when accessing the resource in response to a preflight request.

Access-Control-Expose-Headers

Indicates which headers can be exposed as part of the response by listing their names.

Access-Control-Max-Age

Indicates how long the results of a preflight request can be cached.

Access-Control-Request-Headers

Used when issuing a preflight request to let the server know which HTTP headers will be used when the actual request is made.

Access-Control-Request-Method

Used when issuing a preflight request to let the server know which HTTP method will be used when the actual request is made.

Origin

Indicates where a fetch originates from.

Technical reference

• Fetch specification