pkg/docker/config/config.go
func getPathToAuth(sys *types.SystemContext) (string, error) {
	if sys != nil {
		if sys.AuthFilePath != "" {
			return sys.AuthFilePath, nil
		}
		if sys.RootForImplicitAbsolutePaths != "" {
			return filepath.Join(sys.RootForImplicitAbsolutePaths, fmt.Sprintf(defaultPerUIDPathFormat, os.Getuid())), nil
		}
	}

	runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
	if runtimeDir != "" {
		// This function does not in general need to separately check that the returned path exists; that’s racy, and callers will fail accessing the file anyway.
		// We are checking for os.IsNotExist here only to give the user better guidance what to do in this special case.
		_, err := os.Stat(runtimeDir)
		if os.IsNotExist(err) {
			// This means the user set the XDG_RUNTIME_DIR variable and either forgot to create the directory
			// or made a typo while setting the environment variable,
			// so return an error referring to $XDG_RUNTIME_DIR instead of xdgRuntimeDirPath inside.
			return "", errors.Wrapf(err, "%q directory set by $XDG_RUNTIME_DIR does not exist. Either create the directory or unset $XDG_RUNTIME_DIR.", runtimeDir)
		} // else ignore err and let the caller fail accessing xdgRuntimeDirPath.
		return filepath.Join(runtimeDir, xdgRuntimeDirPath), nil
	}
	return fmt.Sprintf(defaultPerUIDPathFormat, os.Getuid()), nil
}
func getPathToAuth(sys *types.SystemContext) (string, error) {
	if sys != nil {
		if sys.AuthFilePath != "" {
			return sys.AuthFilePath, nil
		}
		if sys.RootForImplicitAbsolutePaths != "" {
			return filepath.Join(sys.RootForImplicitAbsolutePaths, fmt.Sprintf(defaultPerUIDPathFormat, os.Getuid())), nil
		}
	}

	runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
	if runtimeDir != "" {
		// This function does not in general need to separately check that the returned path exists; that’s racy, and callers will fail accessing the file anyway.
		// We are checking for os.IsNotExist here only to give the user better guidance what to do in this special case.
		_, err := os.Stat(runtimeDir)
		if os.IsNotExist(err) {
			// This means the user set the XDG_RUNTIME_DIR variable and either forgot to create the directory
			// or made a typo while setting the environment variable,
			// so return an error referring to $XDG_RUNTIME_DIR instead of xdgRuntimeDirPath inside.
			return "", errors.Wrapf(err, "%q directory set by $XDG_RUNTIME_DIR does not exist. Either create the directory or unset $XDG_RUNTIME_DIR.", runtimeDir)
		} // else ignore err and let the caller fail accessing xdgRuntimeDirPath.
		return filepath.Join(runtimeDir, xdgRuntimeDirPath), nil
	}
	return fmt.Sprintf(defaultPerUIDPathFormat, os.Getuid()), nil
}
// getPath gets the path of the auth.json file
// The path can be overriden by the user if the overwrite-path flag is set
// If the flag is not set and XDG_RUNTIME_DIR is set, the auth.json file is saved in XDG_RUNTIME_DIR/containers
// Otherwise, the auth.json file is stored in /run/containers/UID