OCAPI expects requests and returns responses by default with HTTP version 1.1. However, it is possible to use HTTP version 2 if the instance belongs to the Primary Instance Group (Production, Staging, and Development) or is an On-Demand Sandbox (ODS). This page describes the difference in HTTP header formats regarding the versions.
In HTTP/1.1, header names are case-insensitive, as per RFC 2616, Hypertext Transfer Protocol — HTTP/1.1, Section 4.2:
Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive.
This means that a specific format must not be assumed by the server or client. Therefore, the response may contain header names in a mixed-case format:
In HTTP/2, header names must be lowercase, as per RFC 7540, Hypertext Transfer Protocol Version 2 (HTTP/2), Section 8.1.2:
Just as in HTTP/1.x, header field names are strings of ASCII characters that are compared in a case-insensitive fashion. However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase header field names MUST be treated as malformed (Section 188.8.131.52).
This means that uppercase header names in the request must not be accepted and the response will always have lowercase names:
Usually, HTTP clients capable of HTTP/2 will automatically do the format conversion. But it should be noted that header names have been case-insensitive since the publishing of HTTP/1.1 in 1999. As a consequence, code that behaves as case-sensitive (i.e. it assumes a specific case) should be fixed in order to avoid issues with future HTTP standards.