The autorest package can currently not make use of proxies (specified via lower/upper-case http(s)_proxy environment variables) unless explicitly filling in the Client.Sender field.

Problem description

The tracing module transparently allows proxy support by virtue of using the http.DefaultTransport, which uses ProxyFromEnvironment to re-route traffic via a Http(s) proxy.

Where no Sender is provided explicitly to theClient, transparent proxy support is no longer possible, due to the initialization in sender():

// client.go

// sender returns the Sender to which to send requests.
func (c Client) sender() Sender {
    if c.Sender == nil {
       j, _ := cookiejar.New(nil)
       tracing.Transport.Base = &http.Transport{
                TLSClientConfig: &tls.Config{
                MinVersion: tls.VersionTLS12,
               },
       }
       client := &http.Client{Jar: j, Transport: tracing.Transport}
       return client
    }
    return c.Sender
}

The cause is that, since the Proxy field uses the zero value, the ProxyFromEnvironment, which the http.DefaultTransport uses, no longer applies.

A second, related, problem is that the default timeouts no longer apply.

As a result, proxied requests of code that relies on the default sender currently time out:

Azure.BearerAuthorizer#WithAuthorization: Failed to refresh the Token for request to https://management.azure.com/subscriptions/path/to/resource?api-version=2018-04-01: |
StatusCode=0 -- Original Error: adal: Failed to execute the refresh request.
Error = 'Post https://login.microsoftonline.com/<uuid here>/oauth2/token?api-version=1.0:
dial tcp 40.126.2.38:443: connect: connection timed out

Fix for first problem

We were able to bring back the http.DefaultTransport default using

   tracing.Transport.Base = http.DefaultTransport
   tracing.Transport.Base
    if c.Sender == nil {
       // Use behaviour compatible with DefaultTransport, but require TLS minimum version.
       var baseTransport = *http.DefaultTransport.(*http.Transport)

       baseTransport.TLSClientConfig = &tls.Config{
                MinVersion: tls.VersionTLS12,
       }

       tracing.Transport.Base = &baseTransport
       j, _ := cookiejar.New(nil)
       // ...
     }

However, we then ran into another error (parts redacted as above):

azure.BearerAuthorizer#WithAuthorization: Failed to refresh the Token for request to https://management.azure.com/subscriptions/<uuid here>/resourceGroups/COSMIN/providers/Microsoft.Compute/disks/<diskName>?api-version=2018-04-01: StatusCode=0 -- Original Error: adal: Failed to execute the refresh request. Error = 'Post https://login.microsoftonline.com/<uuid here>/oauth2/token?api-version=1.0: proxyconnect tcp: tls: oversized record received with length 20527

This second error is mysterious - it fails on a standard SQUID proxy configuration using https_proxy=https://proxy:port.