Access-Control-Allow-Origin response header indicates whether the response can be shared with requesting code from the given origin.
|Header type||Response header|
|Forbidden header name||no|
Access-Control-Allow-Origin: * Access-Control-Allow-Origin: <origin> Access-Control-Allow-Origin: null
- For requests without credentials, the literal value "
*" can be specified, as a wildcard; the value tells browsers to allow requesting code from any origin to access the resource. Attempting to use the wildcard with credentials will result in an error.
- Specifies an origin. Only a single origin can be specified. If the server supports clients from multiple origins, it must return the origin for the specific client making the request.
- Specifies the origin "null".
nullshould not be used: "It may seem safe to return
Access-Control-Allow-Origin: "null", but the serialization of the Origin of any resource that uses a non-hierarchical scheme (such as
file:) and sandboxed documents is defined to be "null". Many User Agents will grant such documents access to a response with an
Access-Control-Allow-Origin: "null"header, and any origin can create a hostile document with a "null" Origin. The "null" value for the ACAO header should therefore be avoided."
A response that tells the browser to allow code from any origin to access a resource will include the following:
A response that tells the browser to allow requesting code from the origin
https://developer.mozilla.org to access a resource will include the following:
Limiting the possible
Access-Control-Allow-Origin values to a set of allowed origins requires code on the server side to check the value of the
Origin request header, compare that to a list of allowed origins, and then if the
Origin value is in the list, to set the
Access-Control-Allow-Origin value to the same value as the
If the server sends a response with an
Access-Control-Allow-Origin value that is an explicit origin (rather than the "
*" wildcard), then the response should also include a
Vary response header with the value
Origin — to indicate to browsers that server responses can differ based on the value of the
Origin request header.
Access-Control-Allow-Origin: https://developer.mozilla.org Vary: Origin
The definition of 'Access-Control-Allow-Origin' in that specification.
|Living Standard||Initial definition.|
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