Display message when logging into existing account

internal/config/auth_config_test.go

@@ -387,6 +387,33 @@ func TestLogoutIgnoresErrorsFromConfigAndKeyring(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestUsersForHostNoHost(t *testing.T) {
+	// Given we have a config with no hosts
+	authCfg := newTestAuthConfig(t)
+
+	// When we get the users for a host that doesn't exist
+	_, err := authCfg.UsersForHost("github.com")
+
+	// Then it returns an error
+	require.EqualError(t, err, "unknown host: github.com")
+}
+
+func TestUsersForHostWithUsers(t *testing.T) {
+	// Given we have a config with a host and users
+	authCfg := newTestAuthConfig(t)
+	_, err := authCfg.Login("github.com", "test-user-1", "test-token", "ssh", false)
+	require.NoError(t, err)
+	_, err = authCfg.Login("github.com", "test-user-2", "test-token", "ssh", false)
+	require.NoError(t, err)
+
+	// When we get the users for that host
+	users, err := authCfg.UsersForHost("github.com")
+
+	// Then it succeeds and returns the users
+	require.NoError(t, err)
+	require.Equal(t, []string{"test-user-1", "test-user-2"}, users)
+}
+
 func requireKeyWithValue(t *testing.T, cfg *ghConfig.Config, keys []string, value string) {
 	t.Helper()
 

internal/config/config.go

@@ -373,6 +373,15 @@ func (c *AuthConfig) Logout(hostname, username string) error {
 	return ghConfig.Write(c.cfg)
 }
 
+func (c *AuthConfig) UsersForHost(hostname string) ([]string, error) {
+	users, err := c.cfg.Keys([]string{hostsKey, hostname, usersKey})
+	if err != nil {
+		return nil, fmt.Errorf("unknown host: %s", hostname)
+	}
+
+	return users, nil
+}
+
 func keyringServiceName(hostname string) string {
 	return "gh:" + hostname
 }

pkg/cmd/auth/login/login.go

@@ -177,6 +177,7 @@ func loginRun(opts *LoginOptions) error {
 		if err != nil {
 			return fmt.Errorf("error retrieving current user: %w", err)
 		}
+
 		// Adding a user key ensures that a nonempty host section gets written to the config file.
 		_, loginErr := authCfg.Login(hostname, username, opts.Token, opts.GitProtocol, !opts.InsecureStorage)
 		return loginErr

pkg/cmd/auth/login/login_test.go

@@ -403,7 +403,7 @@ func Test_loginRun_nontty(t *testing.T) {
 			wantSecureToken: "abc123",
 		},
 		{
-			name: "given we are already logged in, a new user is added to the config",
+			name: "given we are already logged in, and log in as a new user, it is added to the config",
 			opts: &LoginOptions{
 				Hostname: "github.com",
 				Token:    "newUserToken",
@@ -677,6 +677,50 @@ func Test_loginRun_Survey(t *testing.T) {
 			wantErrOut:      regexp.MustCompile("Logged in as jillv"),
 			wantSecureToken: "def456",
 		},
+		{
+			name: "given we log in as a user that is already in the config, we get an informational message",
+			opts: &LoginOptions{
+				Hostname:        "github.com",
+				Interactive:     true,
+				InsecureStorage: true,
+			},
+			prompterStubs: func(pm *prompter.PrompterMock) {
+				pm.SelectFunc = func(prompt, _ string, opts []string) (int, error) {
+					switch prompt {
+					case "What is your preferred protocol for Git operations?":
+						return prompter.IndexFor(opts, "HTTPS")
+					case "How would you like to authenticate GitHub CLI?":
+						return prompter.IndexFor(opts, "Paste an authentication token")
+					}
+					return -1, prompter.NoSuchPromptErr(prompt)
+				}
+			},
+			cfgStubs: func(c *config.ConfigMock) {
+				_, err := c.Authentication().Login("github.com", "monalisa", "abc123", "https", false)
+				require.NoError(t, err)
+			},
+			runStubs: func(rs *run.CommandStubber) {
+				rs.Register(`git config credential\.https:/`, 1, "")
+				rs.Register(`git config credential\.helper`, 1, "")
+			},
+			httpStubs: func(reg *httpmock.Registry) {
+				reg.Register(httpmock.REST("GET", ""), httpmock.ScopesResponder("repo,read:org"))
+				reg.Register(
+					httpmock.GraphQL(`query UserCurrent\b`),
+					httpmock.StringResponse(`{"data":{"viewer":{"login":"monalisa"}}}`))
+			},
+			wantHosts: heredoc.Doc(`
+            github.com:
+                users:
+                    monalisa:
+                        oauth_token: def456
+                        git_protocol: https
+                git_protocol: https
+                user: monalisa
+                oauth_token: def456
+            `),
+			wantErrOut: regexp.MustCompile(`! You were already logged in to this account`),
+		},
 	}
 
 	for _, tt := range tests {

pkg/cmd/auth/shared/login_flow.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"slices"
 	"strings"
 
 	"github.com/MakeNowJust/heredoc"
@@ -23,6 +24,7 @@ const defaultSSHKeyTitle = "GitHub CLI"
 
 type iconfig interface {
 	Login(string, string, string, string, bool) (bool, error)
+	UsersForHost(string) ([]string, error)
 }
 
 type LoginOptions struct {
@@ -183,6 +185,15 @@ func Login(opts *LoginOptions) error {
 		}
 	}
 
+	// Get these users before adding the new one, so that we can
+	// check whether the user was already logged in later.
+	//
+	// In this case we ignore the error if the host doesn't exist
+	// because that can occur when the user is logging into a host
+	// for the first time.
+	usersForHost, _ := cfg.UsersForHost(hostname)
+	userWasAlreadyLoggedIn := slices.Contains(usersForHost, username)
+
 	if gitProtocol != "" {
 		fmt.Fprintf(opts.IO.ErrOut, "- gh config set -h %s git_protocol %s\n", hostname, gitProtocol)
 		fmt.Fprintf(opts.IO.ErrOut, "%s Configured git protocol\n", cs.SuccessIcon())
@@ -217,6 +228,10 @@ func Login(opts *LoginOptions) error {
 	}
 
 	fmt.Fprintf(opts.IO.ErrOut, "%s Logged in as %s\n", cs.SuccessIcon(), cs.Bold(username))
+	if userWasAlreadyLoggedIn {
+		fmt.Fprintf(opts.IO.ErrOut, "%s You were already logged in to this account\n", cs.WarningIcon())
+	}
+
 	return nil
 }
 

pkg/cmd/auth/shared/login_flow_test.go

@@ -25,6 +25,10 @@ func (c tinyConfig) Login(host, username, token, gitProtocol string, encrypt boo
 	return false, nil
 }
 
+func (c tinyConfig) UsersForHost(hostname string) ([]string, error) {
+	return nil, nil
+}
+
 func TestLogin_ssh(t *testing.T) {
 	dir := t.TempDir()
 	ios, _, stdout, stderr := iostreams.Test()