Clarify that original and lowerCamelCase field names are allowed for …

…OTLP/JSON

Resolves #2795

This is already the current understanding. This is just a clarification and
describes the behavior explicitly.

CHANGELOG.md

@@ -34,6 +34,8 @@ release.
 
 ### OpenTelemetry Protocol
 
+- Clarify that original and lowerCamelCase field names are allowed for OTLP/JSON
+  ([#2829](https://github.com/open-telemetry/opentelemetry-specification/pull/2829))
 - Add user agent to OTLP exporter specification
   ([#2684](https://github.com/open-telemetry/opentelemetry-specification/pull/2684))
 

specification/protocol/otlp.md

@@ -420,9 +420,14 @@ for mapping between Protobuf and JSON, with the following deviations from that m
   { "kind": 2, ... }
 
 Note that according to [Protobuf specs](
-https://developers.google.com/protocol-buffers/docs/proto3#json) 64-bit integer
-numbers in JSON-encoded payloads are encoded as decimal strings, and either
-numbers or strings are accepted when decoding.
+https://developers.google.com/protocol-buffers/docs/proto3#json):
+
+- 64-bit integer numbers in JSON-encoded payloads are encoded as decimal strings, and
+  either numbers or strings are accepted when decoding.
+
+- Encoders are allowed to produce field names either equal to the original field names
+  declared in the proto files or converted to equivalent lowerCamelCase. Decoders
+  MUST accept both original field names and lowerCamelCase versions.
 
 The client and the server MUST set "Content-Type: application/json" request and
 response headers when sending JSON Protobuf encoded payload.