[CDTOOL-1097] feat(env): Add environment variable for extending the UserAgent string. (#1502)

The environment variable FASTLY_USER_AGENT_EXTENSION can be used to
supply a string which will be inserted into the User-Agent header in
requests sent to the Fastly API; the existing strings representing the
Fastly CLI version and go-fastly version (when applicable) will still be
present.

 All Submissions:

* [X] Have you followed the guidelines in our Contributing document?
* [X] Have you checked to ensure there aren't other open [Pull
Requests](https://github.com/fastly/cli/pulls) for the same
update/change?

Test - before:
```
kpfleming@kpfleming:~/src/fastly/cli$ FASTLY_DEBUG_MODE=true ./fastly whoami


http.Request (dump): "GET /verify HTTP/1.1\r\nHost: api.fastly.com\r\nAccept: application/json\r\nFastly-Key: <redacted>\r\nUser-Agent: FastlyCLI/v0.0.0-unknown\r\n\r\n"
```

Test - after:
```
kpfleming@kpfleming:~/src/fastly/cli$ FASTLY_USER_AGENT_EXTENSION=test1234 FASTLY_DEBUG_MODE=true ./fastly whoami


http.Request (dump): "GET /verify HTTP/1.1\r\nHost: api.fastly.com\r\nAccept: application/json\r\nFastly-Key: <redacted>\r\nUser-Agent: FastlyCLI/v0.0.0-unknown, test1234\r\n\r\n"
```

Author: kpfleming

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 ### Enhancements:
 
+- feat(env): Add environment variable for extending the UserAgent string. ([#1502](https://github.com/fastly/cli/pull/1502))
+
 ### Bug fixes:
 - fix(sso): Ensure that OPTIONS requests sent by browsers do not break SSO authentication. ([#1496](https://github.com/fastly/cli/pull/1496))
 

pkg/app/run.go

@@ -38,6 +38,7 @@ import (
 	"github.com/fastly/cli/pkg/revision"
 	"github.com/fastly/cli/pkg/sync"
 	"github.com/fastly/cli/pkg/text"
+	"github.com/fastly/cli/pkg/useragent"
 )
 
 // Run kick starts the CLI application.
@@ -152,6 +153,18 @@ var Init = func(args []string, stdin io.Reader) (*global.Data, error) {
 		}),
 	}
 
+	// If a UserAgent extension has been set in the environment,
+	// apply it
+	if e.UserAgentExtension != "" {
+		useragent.SetExtension(e.UserAgentExtension)
+	}
+	// Override the go-fastly UserAgent value by prepending the CLI version.
+	//
+	// Results in a header similar to:
+	// User-Agent: FastlyCLI/v11.3.0, FastlyGo/10.5.0 (+github.com/fastly/go-fastly; go1.24.3)
+	// (with any extension supplied above between the FastlyCLI and FastlyGo values)
+	fastly.UserAgent = fmt.Sprintf("%s, %s", useragent.Name, fastly.UserAgent)
+
 	return &global.Data{
 		APIClientFactory: factory,
 		Args:             args,

pkg/commands/version/root.go

@@ -8,23 +8,12 @@ import (
 	"strings"
 	"time"
 
-	"github.com/fastly/go-fastly/v10/fastly"
-
 	"github.com/fastly/cli/pkg/argparser"
 	"github.com/fastly/cli/pkg/github"
 	"github.com/fastly/cli/pkg/global"
 	"github.com/fastly/cli/pkg/revision"
-	"github.com/fastly/cli/pkg/useragent"
 )
 
-func init() {
-	// Override the go-fastly UserAgent value by prepending the CLI version.
-	//
-	// Results in a header similar too:
-	// User-Agent: FastlyCLI/0.1.0, FastlyGo/1.5.0 (1.13.0)
-	fastly.UserAgent = fmt.Sprintf("%s, %s", useragent.Name, fastly.UserAgent)
-}
-
 // RootCommand is the parent command for all subcommands in this package.
 // It should be installed under the primary root command.
 type RootCommand struct {

pkg/config/config.go

@@ -458,9 +458,12 @@ type Environment struct {
 	// UseSSO indicates if user wants to use SSO/OAuth token flow.
 	// 1: enabled, 0: disabled.
 	UseSSO string
-	// WasmMetadataDisable is the env var we look in to disable all data
-	// collection related to a Wasm binary.
-	// Set to "true" to disable all forms of data collection.
+	// UserAgentExtension is the string we'll add to the UserAgent
+	// we send in API requests.
+	UserAgentExtension string
+	// WasmMetadataDisable is the env var we look in to disable
+	// all data collection related to a Wasm binary.  Set to
+	// "true" to disable all forms of data collection.
 	WasmMetadataDisable string
 }
 
@@ -471,6 +474,7 @@ func (e *Environment) Read(state map[string]string) {
 	e.APIToken = state[env.APIToken]
 	e.DebugMode = state[env.DebugMode]
 	e.UseSSO = state[env.UseSSO]
+	e.UserAgentExtension = state[env.UserAgentExtension]
 	e.WasmMetadataDisable = state[env.WasmMetadataDisable]
 }
 

pkg/env/env.go

@@ -40,6 +40,11 @@ const (
 	// Assigned value should be a boolean 1/0 (enable/disable).
 	UseSSO = "FASTLY_USE_SSO"
 
+	// UserAgentExtension informs the CLI of an additional string
+	// which should be added to the UserAgent included in
+	// requests made by the CLI.
+	UserAgentExtension = "FASTLY_USER_AGENT_EXTENSION"
+
 	// WasmMetadataDisable is the env var we look in to disable all data
 	// collection related to a Wasm binary.
 	// Set to "true" to disable all forms of data collection.

pkg/useragent/useragent.go

@@ -8,3 +8,7 @@ import (
 
 // Name is the user agent which we report in all HTTP requests.
 var Name = fmt.Sprintf("%s/%s", "FastlyCLI", revision.AppVersion)
+
+func SetExtension(extension string) {
+	Name = fmt.Sprintf("%s, %s", Name, extension)
+}