/*!
@page gkeconnect-env Environment Variables

A number of environment variables can be used to configure the behavior of
the library. There are also functions to configure this behavior in code. The
environment variables are convenient when troubleshooting problems.

@section gkeconnect-env-endpoint Endpoint Overrides

<!-- inject-endpoint-env-vars-start -->

- `GOOGLE_CLOUD_CPP_GATEWAY_CONTROL_ENDPOINT=...` overrides the
  `EndpointOption` (which defaults to "connectgateway.googleapis.com")
  used by `MakeGatewayControlConnection()`.

<!-- inject-endpoint-env-vars-end -->

@see google::cloud::EndpointOption

@section gkeconnect-env-logging Logging

`GOOGLE_CLOUD_CPP_ENABLE_TRACING=rpc`: turns on tracing for most gRPC
calls. The library injects an additional Stub decorator that prints each gRPC
request and response.  Unless you have configured your own logging backend,
you should also set `GOOGLE_CLOUD_CPP_ENABLE_CLOG` to produce any output on
the program's console.

@see google::cloud::LoggingComponentsOption

`GOOGLE_CLOUD_CPP_TRACING_OPTIONS=...`: modifies the behavior of gRPC tracing,
including whether messages will be output on multiple lines, or whether
string/bytes fields will be truncated.

@see google::cloud::GrpcTracingOptionsOption

`GOOGLE_CLOUD_CPP_ENABLE_CLOG=yes`: turns on logging in the library, basically
the library always "logs" but the logging infrastructure has no backend to
actually print anything until the application sets a backend or they set this
environment variable.

@see google::cloud::LogBackend
@see google::cloud::LogSink

@section gkeconnect-env-project Setting the Default Project

`GOOGLE_CLOUD_PROJECT=...`: is used in examples and integration tests to
configure the GCP project. This has no effect in the library.

*/
