feat(sg): add command to generate a dotcom user gateway access token (#63125)

We can now generate gateway access tokens from sg instead of having to
manually wrangle a script to do it every time. This will help with
making Cody Gateway easier to run locally.

## Test plan
Tested locally.

---------

Co-authored-by: William Bezuidenhout <william.bezuidenhout@sourcegraph.com>

dev/sg/BUILD.bazel

@@ -15,6 +15,7 @@ go_library(
         "sg_backport.go",
         "sg_bazel.go",
         "sg_cloud.go",
+        "sg_cody_gateway.go",
         "sg_db.go",
         "sg_deploy.go",
         "sg_doctor.go",
@@ -82,6 +83,7 @@ go_library(
         "//dev/sg/root",
         "//dev/sg/sams",
         "//dev/team",
+        "//internal/accesstoken",
         "//internal/database",
         "//internal/database/basestore",
         "//internal/database/connections/live",

dev/sg/main.go

@@ -9,9 +9,8 @@ import (
 	"time"
 
 	hashstructure "github.com/mitchellh/hashstructure/v2"
-	"github.com/urfave/cli/v2"
-
 	"github.com/sourcegraph/log"
+	"github.com/urfave/cli/v2"
 
 	"github.com/sourcegraph/sourcegraph/dev/sg/ci"
 	"github.com/sourcegraph/sourcegraph/dev/sg/internal/analytics"
@@ -312,6 +311,7 @@ var sg = &cli.App{
 		release.Command,
 		updateCommand,
 		versionCommand,
+		codyGatewayCommand,
 	},
 	ExitErrHandler: func(cmd *cli.Context, err error) {
 		interrupt.Wait()

dev/sg/sg_cody_gateway.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"os"
+	"strings"
+
+	"github.com/urfave/cli/v2"
+
+	"github.com/sourcegraph/sourcegraph/dev/sg/internal/category"
+	"github.com/sourcegraph/sourcegraph/dev/sg/internal/std"
+	"github.com/sourcegraph/sourcegraph/internal/accesstoken"
+	"github.com/sourcegraph/sourcegraph/lib/errors"
+)
+
+var codyGatewayCommand = &cli.Command{
+	Name:     "cody-gateway",
+	Usage:    "set of commands that are helpful for working with Cody Gateway locally",
+	Category: category.Util,
+	Subcommands: []*cli.Command{{
+		Name:        "gen-token",
+		Usage:       "generate a new token for use with Cody Gateway",
+		UsageText:   "sg cody-gateway gen-token [sg token]",
+		Description: "generates a token with the given `sg token` - which should be prefixed with `sgp_`",
+		Action:      genGatewayAccessTokenExec,
+	}},
+}
+
+func genGatewayAccessTokenExec(c *cli.Context) error {
+	out := std.NewOutput(os.Stderr, false)
+	if c.NArg() == 0 {
+		out.WriteWarningf("The first argument should be a Sourcegraph private access token - see --help for more information")
+		return errors.New("missing private access token argument")
+	}
+
+	out.WriteNoticef("Generating new gateway access token ...")
+	privateToken := c.Args().Get(0)
+	if !strings.HasPrefix(privateToken, "sgp_") {
+		out.WriteWarningf("Token must be prefixed with \"sgp_\"")
+		return errors.New("invalid token: not prefixed with sgp_")
+	}
+	accessToken, err := accesstoken.GenerateDotcomUserGatewayAccessToken(privateToken)
+	if err != nil {
+		return errors.Newf("failed to generate gateway access token: %s", err)
+	}
+	std.Out.Write(accessToken)
+	return nil
+}