Add auth setup-git for setting up gh as a git credential helper (#4246)

Adds a new command `gh auth setup-git [<hostname>]` that sets up git to
use the GitHub CLI as a credential helper.

The gist is that it runs these two git commands for each hostname the
user is authenticated with.

```
git config --global --replace-all 'credential.https://github.com.helper' ''
git config --global --add 'credential.https://github.com.helper' '!gh auth git-credential'
```

If a hostname flag is given, it'll setup GH CLI as a credential helper
for only that hostname.

If the user is not authenticated with any git hostnames, or the user is
not authenticated with the hostname given as a flag, it'll print an
error.

Co-authored-by: Mislav Marohnić <mislav@github.com>

pkg/cmd/auth/auth.go

@@ -5,6 +5,7 @@ import (
 	authLoginCmd "github.com/cli/cli/v2/pkg/cmd/auth/login"
 	authLogoutCmd "github.com/cli/cli/v2/pkg/cmd/auth/logout"
 	authRefreshCmd "github.com/cli/cli/v2/pkg/cmd/auth/refresh"
+	authSetupGitCmd "github.com/cli/cli/v2/pkg/cmd/auth/setupgit"
 	authStatusCmd "github.com/cli/cli/v2/pkg/cmd/auth/status"
 	"github.com/cli/cli/v2/pkg/cmdutil"
 	"github.com/spf13/cobra"
@@ -24,6 +25,7 @@ func NewCmdAuth(f *cmdutil.Factory) *cobra.Command {
 	cmd.AddCommand(authStatusCmd.NewCmdStatus(f, nil))
 	cmd.AddCommand(authRefreshCmd.NewCmdRefresh(f, nil))
 	cmd.AddCommand(gitCredentialCmd.NewCmdCredential(f, nil))
+	cmd.AddCommand(authSetupGitCmd.NewCmdSetupGit(f, nil))
 
 	return cmd
 }

pkg/cmd/auth/setupgit/setupgit.go

@@ -0,0 +1,100 @@
+package setupgit
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/cli/cli/v2/internal/config"
+	"github.com/cli/cli/v2/pkg/cmd/auth/shared"
+	"github.com/cli/cli/v2/pkg/cmdutil"
+	"github.com/cli/cli/v2/pkg/iostreams"
+	"github.com/spf13/cobra"
+)
+
+type gitConfigurator interface {
+	Setup(hostname, username, authToken string) error
+}
+
+type SetupGitOptions struct {
+	IO           *iostreams.IOStreams
+	Config       func() (config.Config, error)
+	Hostname     string
+	gitConfigure gitConfigurator
+}
+
+func NewCmdSetupGit(f *cmdutil.Factory, runF func(*SetupGitOptions) error) *cobra.Command {
+	opts := &SetupGitOptions{
+		IO:     f.IOStreams,
+		Config: f.Config,
+	}
+
+	cmd := &cobra.Command{
+		Short: "Configure git to use GitHub CLI as a credential helper",
+		Use:   "setup-git",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			opts.gitConfigure = &shared.GitCredentialFlow{
+				Executable: f.Executable(),
+			}
+
+			if runF != nil {
+				return runF(opts)
+			}
+			return setupGitRun(opts)
+		},
+	}
+
+	cmd.Flags().StringVarP(&opts.Hostname, "hostname", "h", "", "The hostname to configure git for")
+
+	return cmd
+}
+
+func setupGitRun(opts *SetupGitOptions) error {
+	cfg, err := opts.Config()
+	if err != nil {
+		return err
+	}
+
+	hostnames, err := cfg.Hosts()
+	if err != nil {
+		return err
+	}
+
+	stderr := opts.IO.ErrOut
+	cs := opts.IO.ColorScheme()
+
+	if len(hostnames) == 0 {
+		fmt.Fprintf(
+			stderr,
+			"You are not logged into any GitHub hosts. Run %s to authenticate.\n",
+			cs.Bold("gh auth login"),
+		)
+
+		return cmdutil.SilentError
+	}
+
+	hostnamesToSetup := hostnames
+
+	if opts.Hostname != "" {
+		if !has(opts.Hostname, hostnames) {
+			return fmt.Errorf("You are not logged into the GitHub host %q\n", opts.Hostname)
+		}
+		hostnamesToSetup = []string{opts.Hostname}
+	}
+
+	for _, hostname := range hostnamesToSetup {
+		if err := opts.gitConfigure.Setup(hostname, "", ""); err != nil {
+			return fmt.Errorf("failed to set up git credential helper: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func has(needle string, haystack []string) bool {
+	for _, s := range haystack {
+		if strings.EqualFold(s, needle) {
+			return true
+		}
+	}
+	return false
+}

pkg/cmd/auth/setupgit/setupgit_test.go

@@ -0,0 +1,122 @@
+package setupgit
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/cli/cli/v2/internal/config"
+	"github.com/cli/cli/v2/pkg/iostreams"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type mockGitConfigurer struct {
+	setupErr error
+}
+
+func (gf *mockGitConfigurer) Setup(hostname, username, authToken string) error {
+	return gf.setupErr
+}
+
+func Test_setupGitRun(t *testing.T) {
+	tests := []struct {
+		name           string
+		opts           *SetupGitOptions
+		expectedErr    string
+		expectedErrOut string
+	}{
+		{
+			name: "opts.Config returns an error",
+			opts: &SetupGitOptions{
+				Config: func() (config.Config, error) {
+					return nil, fmt.Errorf("oops")
+				},
+			},
+			expectedErr: "oops",
+		},
+		{
+			name:           "no authenticated hostnames",
+			opts:           &SetupGitOptions{},
+			expectedErr:    "SilentError",
+			expectedErrOut: "You are not logged into any GitHub hosts. Run gh auth login to authenticate.\n",
+		},
+		{
+			name: "not authenticated with the hostname given as flag",
+			opts: &SetupGitOptions{
+				Hostname: "foo",
+				Config: func() (config.Config, error) {
+					cfg := config.NewBlankConfig()
+					require.NoError(t, cfg.Set("bar", "", ""))
+					return cfg, nil
+				},
+			},
+			expectedErr:    "You are not logged into the GitHub host \"foo\"\n",
+			expectedErrOut: "",
+		},
+		{
+			name: "error setting up git for hostname",
+			opts: &SetupGitOptions{
+				gitConfigure: &mockGitConfigurer{
+					setupErr: fmt.Errorf("broken"),
+				},
+				Config: func() (config.Config, error) {
+					cfg := config.NewBlankConfig()
+					require.NoError(t, cfg.Set("bar", "", ""))
+					return cfg, nil
+				},
+			},
+			expectedErr:    "failed to set up git credential helper: broken",
+			expectedErrOut: "",
+		},
+		{
+			name: "no hostname option given. Setup git for each hostname in config",
+			opts: &SetupGitOptions{
+				gitConfigure: &mockGitConfigurer{},
+				Config: func() (config.Config, error) {
+					cfg := config.NewBlankConfig()
+					require.NoError(t, cfg.Set("bar", "", ""))
+					return cfg, nil
+				},
+			},
+		},
+		{
+			name: "setup git for the hostname given via options",
+			opts: &SetupGitOptions{
+				Hostname:     "yes",
+				gitConfigure: &mockGitConfigurer{},
+				Config: func() (config.Config, error) {
+					cfg := config.NewBlankConfig()
+					require.NoError(t, cfg.Set("bar", "", ""))
+					require.NoError(t, cfg.Set("yes", "", ""))
+					return cfg, nil
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.opts.Config == nil {
+				tt.opts.Config = func() (config.Config, error) {
+					return config.NewBlankConfig(), nil
+				}
+			}
+
+			io, _, _, stderr := iostreams.Test()
+
+			io.SetStdinTTY(true)
+			io.SetStderrTTY(true)
+			io.SetStdoutTTY(true)
+			tt.opts.IO = io
+
+			err := setupGitRun(tt.opts)
+			if tt.expectedErr != "" {
+				assert.EqualError(t, err, tt.expectedErr)
+			} else {
+				assert.NoError(t, err)
+			}
+
+			assert.Equal(t, tt.expectedErrOut, stderr.String())
+		})
+	}
+}

pkg/cmd/auth/shared/git_credential.go

@@ -64,7 +64,7 @@ func (flow *GitCredentialFlow) Setup(hostname, username, authToken string) error
 func (flow *GitCredentialFlow) gitCredentialSetup(hostname, username, password string) error {
 	if flow.helper == "" {
 		// first use a blank value to indicate to git we want to sever the chain of credential helpers
-		preConfigureCmd, err := git.GitCommand("config", "--global", gitCredentialHelperKey(hostname), "")
+		preConfigureCmd, err := git.GitCommand("config", "--global", "--replace-all", gitCredentialHelperKey(hostname), "")
 		if err != nil {
 			return err
 		}

pkg/cmd/auth/shared/git_credential_test.go

@@ -25,7 +25,7 @@ func TestGitCredentialSetup_configureExisting(t *testing.T) {
 func TestGitCredentialSetup_setOurs(t *testing.T) {
 	cs, restoreRun := run.Stub()
 	defer restoreRun(t)
-	cs.Register(`git config --global credential\.`, 0, "", func(args []string) {
+	cs.Register(`git config --global --replace-all credential\.`, 0, "", func(args []string) {
 		if key := args[len(args)-2]; key != "credential.https://example.com.helper" {
 			t.Errorf("git config key was %q", key)
 		}