1. Google Cloud Apigee Documentation
"Extract Variables policy": Under the element description
the documentation states: "The message must be parsed as JSON by Apigee. If the message is not valid JSON
or if the message is not parsed as JSON for other reasons (such as the Content-type header not being application/json)
the policy will not be able to extract any variables." This directly confirms that the Content-Type header must be application/json.
Source: Google Cloud Documentation > Apigee > Reference > Policies > Extract Variables policy reference.
2. IETF RFC 8259
"The JavaScript Object Notation (JSON) Data Interchange Format": This official standard defines the media type for JSON.
Section 11
"IANA Considerations": "The MIME media type for JSON text is application/json." This establishes application/json as the correct and standard value.