feat: add external-auth cli (#10052)

* feat: add `external-auth` cli

* Add subcommands

* Improve descriptions

* Add external-auth subcommand

* Fix docs

* Fix gen

* Fix comment

* Fix golden file

cli/externalauth.go

@@ -0,0 +1,91 @@
+package cli
+
+import (
+	"os/signal"
+
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/cli/clibase"
+	"github.com/coder/coder/v2/cli/cliui"
+	"github.com/coder/coder/v2/codersdk/agentsdk"
+)
+
+func (r *RootCmd) externalAuth() *clibase.Cmd {
+	return &clibase.Cmd{
+		Use:   "external-auth",
+		Short: "Manage external authentication",
+		Long:  "Authenticate with external services inside of a workspace.",
+		Handler: func(i *clibase.Invocation) error {
+			return i.Command.HelpHandler(i)
+		},
+		Children: []*clibase.Cmd{
+			r.externalAuthAccessToken(),
+		},
+	}
+}
+
+func (r *RootCmd) externalAuthAccessToken() *clibase.Cmd {
+	var silent bool
+	return &clibase.Cmd{
+		Use:   "access-token <provider>",
+		Short: "Print auth for an external provider",
+		Long: "Print an access-token for an external auth provider. " +
+			"The access-token will be validated and sent to stdout with exit code 0. " +
+			"If a valid access-token cannot be obtained, the URL to authenticate will be sent to stdout with exit code 1\n" + formatExamples(
+			example{
+				Description: "Ensure that the user is authenticated with GitHub before cloning.",
+				Command: `#!/usr/bin/env sh
+
+OUTPUT=$(coder external-auth access-token github)
+if [ $? -eq 0 ]; then
+  echo "Authenticated with GitHub"
+else
+  echo "Please authenticate with GitHub:"
+  echo $OUTPUT
+fi
+`,
+			},
+		),
+		Options: clibase.OptionSet{{
+			Name:        "Silent",
+			Flag:        "s",
+			Description: "Do not print the URL or access token.",
+			Value:       clibase.BoolOf(&silent),
+		}},
+
+		Handler: func(inv *clibase.Invocation) error {
+			ctx := inv.Context()
+
+			ctx, stop := signal.NotifyContext(ctx, InterruptSignals...)
+			defer stop()
+
+			client, err := r.createAgentClient()
+			if err != nil {
+				return xerrors.Errorf("create agent client: %w", err)
+			}
+
+			token, err := client.ExternalAuth(ctx, agentsdk.ExternalAuthRequest{
+				ID: inv.Args[0],
+			})
+			if err != nil {
+				return xerrors.Errorf("get external auth token: %w", err)
+			}
+
+			if !silent {
+				if token.URL != "" {
+					_, err = inv.Stdout.Write([]byte(token.URL))
+				} else {
+					_, err = inv.Stdout.Write([]byte(token.AccessToken))
+				}
+				if err != nil {
+					return err
+				}
+			}
+
+			if token.URL != "" {
+				return cliui.Canceled
+			}
+			return nil
+		},
+	}
+}