[receiver/otlpreceiver] errorHandler returns 500 when Content-Type is unsupported or malformed

Component(s)

No response

Describe the issue you're reporting

Describe the bug

errorHandler in receiver/otlpreceiver/otlphttp.go encodes the error Status using the request's Content-Type. When that type is neither protobuf nor JSON — unsupported (text/plain) or malformed (application/) — it drops the original status code and writes 500 {"code": 13, "message": "failed to marshal error message"}. Client errors such as a 401 from an auth extension are reported as server faults, so clients retry requests that can never succeed.

Steps to reproduce

Collector with the OTLP receiver and an authenticator on the HTTP endpoint:

  curl -i -X POST localhost:4318/v1/traces \
    -H 'Content-Type: text/plain' \
    -H 'Authorization: Bearer auth_thisisnotarealtoken' \
    --data-binary ''

What did you expect to see?

401 Unauthorized, status message encoded as JSON.

What did you see instead?

500 Internal Server Error with {"code": 13, "message": "failed to marshal error message"}.

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