fix: ensure we are talking to coder on first user check (#11130)

cli/login_test.go

@@ -3,6 +3,8 @@ package cli_test
 import (
 	"context"
 	"fmt"
+	"net/http"
+	"net/http/httptest"
 	"runtime"
 	"testing"
 
@@ -36,6 +38,39 @@ func TestLogin(t *testing.T) {
 		require.ErrorContains(t, err, errMsg)
 	})
 
+	t.Run("InitialUserNonCoderURLFail", func(t *testing.T) {
+		t.Parallel()
+
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusNotFound)
+			w.Write([]byte("Not Found"))
+		}))
+		defer ts.Close()
+
+		badLoginURL := ts.URL
+		root, _ := clitest.New(t, "login", badLoginURL)
+		err := root.Run()
+		errMsg := fmt.Sprintf("Failed to check server %q for first user, is the URL correct and is coder accessible from your browser?", badLoginURL)
+		require.ErrorContains(t, err, errMsg)
+	})
+
+	t.Run("InitialUserNonCoderURLSuccess", func(t *testing.T) {
+		t.Parallel()
+
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("X-Coder-Build-Version", "something")
+			w.WriteHeader(http.StatusNotFound)
+			w.Write([]byte("Not Found"))
+		}))
+		defer ts.Close()
+
+		badLoginURL := ts.URL
+		root, _ := clitest.New(t, "login", badLoginURL)
+		err := root.Run()
+		// this means we passed the check for a valid coder server
+		require.ErrorContains(t, err, "the initial user cannot be created in non-interactive mode")
+	})
+
 	t.Run("InitialUserTTY", func(t *testing.T) {
 		t.Parallel()
 		client := coderdtest.New(t, nil)

codersdk/users.go

@@ -190,7 +190,15 @@ func (c *Client) HasFirstUser(ctx context.Context) (bool, error) {
 		return false, err
 	}
 	defer res.Body.Close()
+
 	if res.StatusCode == http.StatusNotFound {
+		// ensure we are talking to coder and not
+		// some other service that returns 404
+		v := res.Header.Get("X-Coder-Build-Version")
+		if v == "" {
+			return false, xerrors.Errorf("missing build version header, not a coder instance")
+		}
+
 		return false, nil
 	}
 	if res.StatusCode != http.StatusOK {