How to use the identify.identify.license_id function in identify

cfg['metadata']['long_description'] = long_description

        tags = identify.tags_from_filename(readme)
        if 'markdown' in tags:
            cfg['metadata']['long_description_content_type'] = 'text/markdown'
        elif 'rst' in tags:
            cfg['metadata']['long_description_content_type'] = 'text/x-rst'
        else:
            cfg['metadata']['long_description_content_type'] = 'text/plain'

    # set license fields if a license exists
    license_filename = _first_file(filename, 'licen[sc]e')
    if license_filename is not None:
        cfg['metadata']['license_file'] = os.path.basename(license_filename)

        license_id = identify.license_id(license_filename)
        if license_id is not None:
            cfg['metadata']['license'] = license_id

        if license_id in LICENSE_TO_CLASSIFIER:
            cfg['metadata']['classifiers'] = (
                cfg['metadata'].get('classifiers', '').rstrip() +
                f'\n{LICENSE_TO_CLASSIFIER[license_id]}'
            )

    requires = _python_requires(filename, min_py3_version=min_py3_version)
    if requires is not None:
        if not cfg.has_section('options'):
            cfg.add_section('options')
        cfg['options']['python_requires'] = requires

    install_requires = _requires(cfg, 'install_requires')