It looks like support for an alternative to the default TRACER_STATE_HEADER_NAME defined in constant.js has been added to tracer.js and text_map_code.js by allowing a 'contextKey' to be passed as an option. However, the initTracer method in configuration.js does not include support for this when creating a new Tracer object. The current code reads like this:

return new Tracer(config.serviceName, reporter, sampler, { metrics: options.metrics, logger: options.logger, tags: options.tags, });

Fixing this seems like a simple update - something like this:

return new Tracer(config.serviceName, reporter, sampler, { metrics: options.metrics, logger: options.logger, tags: options.tags, contextKey: options.contextKey });

Is there a reason that contextKey is not supported in the initTracer method?