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

Open Source Vulnerabilities CVE-2024-28110

Go SDK for CloudEvents is the official CloudEvents SDK to integrate applications with CloudEvents. Prior to version 2.15.2, using cloudevents.WithRoundTripper to create a cloudevents.Client with an authenticated http.RoundTripper causes the go-sdk to leak credentials to arbitrary endpoints. When the transport is populated with an authenticated 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. Version 2.15.2 patches this issue.

Open Source Vulnerabilities GHSA-5pf6-2qwx-pxm2

### 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](https://github.com/cloudevents/sdk-go/blob/67e389964131d55d65cd14b4eb32d57a47312695/v2/protocol/http/protocol.go#L104-L110) (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](https://pkg.go.dev/golang.org/x/oauth2#Transport) - [idtoken.NewClient(...).Transport](https://pkg.go.dev/google.golang.org/api/idtoken#NewClient) ... 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

Open Source Vulnerabilities GO-2024-2618

Using cloudevents.WithRoundTripper to create a cloudevents.Client with an authenticated http.RoundTripper causes the go-sdk to leak credentials to arbitrary endpoints. When the transport is populated with an authenticated transport, http.DefaultClient is modified with the authenticated transport and will start to send Authorization tokens to any endpoint it is used to contact.