Go SDK for CloudEvents's use of WithRoundTripper to create a Client leaks credentials

Impact

What kind of vulnerability is it? Who is impacted?
Using cloudevents.WithRoundTripper to create a cloudevents.Client with an authenticated http.RoundTripper causes the go-sdk to leak credentials to arbitrary endpoints.

The relevant code is here (also inline, emphasis added):

<pre>if p.Client == nil {
p.Client = http.DefaultClient
}

if p.roundTripper != nil {
p.Client.Transport = p.roundTripper
}
</pre>

When the transport is populated with an authenticated transport such as:

• oauth2.Transport
• idtoken.NewClient(…).Transport

… then http.DefaultClient is modified with the authenticated transport and will start to send Authorization tokens to
any endpoint it is used to contact!

Found and patched by: @tcnghia and @mattmoor

Patches

v.2.15.2