HTTP requests and responses may be transmitted between cloud-based application instances. Each outgoing HTTP request may include authentication credentials and an “X-Snc-Integration-Source” header that identifies the source of the request. A table of approved users may be maintained, including each user's authentication credentials and one or more source instances from which they are expected to generate HTTP requests. When the HTTP request is received, the HTTP request will be parsed to identify the authentication credentials and the source of the request. The table of authorized users is then referenced to determine if the authentication credentials and the source of the request match those of an authorized user. If the authentication credentials and the source of the request match those of an authorized user, access will be granted. If the authentication credentials and the source of the request do not match those of an authorized user, access will be denied.