google-fonts.txt

Things we do allow

The links:
https://fonts.googleapis.com/css
//fonts.googleapis.com/css
https://ajax.googleapis.com/ajax/libs/webfont/1.6.26/webfont.js
https://fonts.gstatic.com


The code examples:
Notes:
Examples are separated with ----. 
We need to cover both wp_register_style and wp_enqueue_style

function twentyseventeen_fonts_url() {
	$fonts_url = '';

	/*
	 * Translators: If there are characters in your language that are not
	 * supported by Libre Franklin, translate this to 'off'. Do not translate
	 * into your own language.
	 */
	$libre_franklin = _x( 'on', 'Libre Franklin font: on or off', 'twentyseventeen' );

	if ( 'off' !== $libre_franklin ) {
		$font_families = array();

		$font_families[] = 'Libre Franklin:300,300i,400,400i,600,600i,800,800i';

		$query_args = array(
			'family' => urlencode( implode( '|', $font_families ) ),
			'subset' => urlencode( 'latin,latin-ext' ),
		);

		$fonts_url = add_query_arg( $query_args, 'https://fonts.googleapis.com/css' );
	}

	return esc_url_raw( $fonts_url );
}

----

function twentyseventeen_resource_hints( $urls, $relation_type ) {
	if ( wp_style_is( 'twentyseventeen-fonts', 'queue' ) && 'preconnect' === $relation_type ) {
		$urls[] = array(
			'href' => 'https://fonts.gstatic.com',
			'crossorigin',
		);
	}

	return $urls;
}

----

This is only a partial of a PHP file in Kirki:
kirki/modules/webfonts/webfonts.php

 return array("kind" => "webfonts#webfontList", "items" => array(array("kind" => "webfonts#webfont", "family" => "ABeeZee", "category" => "sans-serif", 
 "variants" => array("regular", "italic"), "subsets" => array("latin"), 
 "version" => "v11", "lastModified" => "2017-10-10", 
 "files" => array("regular" => "http://fonts.gstatic.com/s/abeezee/v11/mE5BOuZKGln_Ex0uYKpIaw.ttf", 
 "italic" => "http://fonts.gstatic.com/s/abeezee/v11/kpplLynmYgP0YtlJA3atRw.ttf")),

----

if ( ! function_exists( 'ot_load_google_fonts_css' ) ) {

  function ot_load_google_fonts_css() {

    /* don't load in the admin */
    if ( is_admin() )
      return;

    $ot_google_fonts      = get_theme_mod( 'ot_google_fonts', array() );
    $ot_set_google_fonts  = get_theme_mod( 'ot_set_google_fonts', array() );
    $families             = array();
    $subsets              = array();
    $append               = '';

    if ( ! empty( $ot_set_google_fonts ) ) {

      foreach( $ot_set_google_fonts as $id => $fonts ) {

        foreach( $fonts as $font ) {

          // Can't find the font, bail!
          if ( ! isset( $ot_google_fonts[$font['family']]['family'] ) ) {
            continue;
          }

          // Set variants & subsets
          if ( ! empty( $font['variants'] ) && is_array( $font['variants'] ) ) {

            // Variants string
            $variants = ':' . implode( ',', $font['variants'] );

            // Add subsets to array
            if ( ! empty( $font['subsets'] ) && is_array( $font['subsets'] ) ) {
              foreach( $font['subsets'] as $subset ) {
                $subsets[] = $subset;
              }
            }

          }

          // Add family & variants to array
          if ( isset( $variants ) ) {
            $families[] = str_replace( ' ', '+', $ot_google_fonts[$font['family']]['family'] ) . $variants;
          }

        }

      }

    }

    if ( ! empty( $families ) ) {

      $families = array_unique( $families );

      // Append all subsets to the path, unless the only subset is latin.
      if ( ! empty( $subsets ) ) {
        $subsets = implode( ',', array_unique( $subsets ) );
        if ( $subsets != 'latin' ) {
          $append = '&subset=' . $subsets;
        }
      }

      wp_enqueue_style( 'ot-google-fonts', esc_url( '//fonts.googleapis.com/css?family=' . implode( '|', $families ) ) . $append, false, null );
    }

  }

}

----

wp_register_style( 'google_fonts', '//fonts.googleapis.com/css?family=Lato' );

----

if (!function_exists('qqq_scripts')) {
	function qqq_scripts() {
		wp_enqueue_style('qqq-google-fonts', 'https://fonts.googleapis.com/css?family=Open+Sans:400,400italic,700,600', array(), null);
	}
}
add_action('wp_enqueue_scripts', 'qqq_scripts');

----

wp_enqueue_script(
                    'webfontloader',
                    'https://ajax.googleapis.com/ajax/libs/webfont/1.5.0/webfont.js',
                    array( 'jquery' ),
                    '1.5.0',
                    true
                );

----

Note that this is inside a PHP file:

<script>
/* You can add more configuration options to webfontloader by previously defining the WebFontConfig with your options */
if ( typeof WebFontConfig === "undefined" ) {
    WebFontConfig = new Object();
 }
WebFontConfig['google'] = {families: [<?php echo $typography->makeGoogleWebfontString ( $this->typography ) ?>]};

(function() {
var wf = document.createElement( 'script' );
 wf.src = 'https://ajax.googleapis.com/ajax/libs/webfont/1.5.3/webfont.js';
wf.type = 'text/javascript';
wf.async = 'true';
var s = document.getElementsByTagName( 'script' )[0];
s.parentNode.insertBefore( wf, s );
})();
</script>

----

The following is a partial from a JSON file:
premier/inc/fonts.json
 "files": {
    "300": "http://fonts.gstatic.com/s/opensans/v10/DXI1ORHCpsQm3Vp6mXoaTS3USBnSvpkopQaUR-2r7iU.ttf",
    "300italic": "http://fonts.gstatic.com/s/opensans/v10/PRmiXeptR36kaC0GEAetxi9-WlPSxbfiI49GsXo3q0g.ttf",
    "regular": "http://fonts.gstatic.com/s/opensans/v10/IgZJs4-7SA1XX_edsoXWog.ttf",
    "italic": "http://fonts.gstatic.com/s/opensans/v10/O4NhV7_qs9r9seTo7fnsVKCWcynf_cDxXwCLxiixG1c.ttf",
    "600": "http://fonts.gstatic.com/s/opensans/v10/MTP_ySUJH_bn48VBG8sNSi3USBnSvpkopQaUR-2r7iU.ttf",
    "600italic": "http://fonts.gstatic.com/s/opensans/v10/PRmiXeptR36kaC0GEAetxpZ7xm-Bj30Bj2KNdXDzSZg.ttf",
    "700": "http://fonts.gstatic.com/s/opensans/v10/k3k702ZOKiLJc3WVjuplzC3USBnSvpkopQaUR-2r7iU.ttf",
    "700italic": "http://fonts.gstatic.com/s/opensans/v10/PRmiXeptR36kaC0GEAetxne1Pd76Vl7zRpE7NLJQ7XU.ttf",
    "800": "http://fonts.gstatic.com/s/opensans/v10/EInbV5DfGHOiMmvb1Xr-hi3USBnSvpkopQaUR-2r7iU.ttf",
    "800italic": "http://fonts.gstatic.com/s/opensans/v10/PRmiXeptR36kaC0GEAetxg89PwPrYLaRFJ-HNCU9NbA.ttf"
}