The canonical form of an API key: trimmed, and undefined when blank (a blank
key means "no key", so no X-API-Key header is sent). Idempotent. Trimming comes
before the header check (headerValueProblem), so a key read from a CRLF file
("k\r") is the same key from the client, the env var and the CLI flag.
A non-string is returned as is, for the header check to reject.
The canonical form of an API key: trimmed, and
undefinedwhen blank (a blank key means "no key", so no X-API-Key header is sent). Idempotent. Trimming comes before the header check (headerValueProblem), so a key read from a CRLF file ("k\r") is the same key from the client, the env var and the CLI flag. A non-string is returned as is, for the header check to reject.