fix: use expires_in field for git device refresh (#8411)

This was causing git auth to never refresh after the token
became expired after 8hrs.

coderd/gitauth/oauth.go

@@ -6,11 +6,13 @@ import (
 	"net/http"
 	"net/url"
 	"regexp"
+	"time"
 
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/github"
 	"golang.org/x/xerrors"
 
+	"github.com/coder/coder/coderd/database"
 	"github.com/coder/coder/codersdk"
 )
 
@@ -138,7 +140,9 @@ func (c *DeviceAuth) AuthorizeDevice(ctx context.Context) (*codersdk.GitAuthDevi
 }
 
 type ExchangeDeviceCodeResponse struct {
-	*oauth2.Token
+	AccessToken      string `json:"access_token"`
+	RefreshToken     string `json:"refresh_token"`
+	ExpiresIn        int    `json:"expires_in"`
 	Error            string `json:"error"`
 	ErrorDescription string `json:"error_description"`
 }
@@ -175,7 +179,11 @@ func (c *DeviceAuth) ExchangeDeviceCode(ctx context.Context, deviceCode string)
 	if body.Error != "" {
 		return nil, xerrors.New(body.Error)
 	}
-	return body.Token, nil
+	return &oauth2.Token{
+		AccessToken:  body.AccessToken,
+		RefreshToken: body.RefreshToken,
+		Expiry:       database.Now().Add(time.Duration(body.ExpiresIn) * time.Second),
+	}, nil
 }
 
 func (c *DeviceAuth) formatDeviceTokenURL(deviceCode string) (string, error) {

coderd/gitauth_test.go

@@ -200,9 +200,7 @@ func TestGitAuthDevice(t *testing.T) {
 		require.Equal(t, "authorization_pending", sdkErr.Detail)
 
 		resp = gitauth.ExchangeDeviceCodeResponse{
-			Token: &oauth2.Token{
-				AccessToken: "hey",
-			},
+			AccessToken: "hey",
 		}
 
 		err = client.GitAuthDeviceExchange(context.Background(), "test", codersdk.GitAuthDeviceExchange{