web.config

<?xml version="1.0"?>
<configuration>
  <system.web>
    <compilation debug="false" targetFramework="4.0" />
  </system.web>
  <system.webServer>
    <urlCompression doStaticCompression="true" doDynamicCompression="true" dynamicCompressionBeforeCache="false" />

    <!-- add a mime type for br, otherwise we get 404 -->
    <staticContent>
      <remove fileExtension=".br" />
      <mimeMap fileExtension=".br" mimeType="application/brotli" />
    </staticContent>

    <rewrite>
      <rewriteMaps>
        <!-- pre-compressed files will be suffixed with br or gz -->
        <!-- map of correct mime types to be restored -->
        <rewriteMap name="CompressedExtensions" defaultValue="">
          <add key="js.gz" value="application/javascript" />
          <add key="css.gz" value="text/css" />
          <add key="js.br" value="application/javascript" />
          <add key="css.br" value="text/css" />
        </rewriteMap>
      </rewriteMaps>
      <rules>
        <rule name="ServerPreCompressedBrotli" stopProcessing="true">
          <match url="^(.*/)?(.*?)\.(css|js)([?#].*)?$" />
          <conditions>
            <!-- client accepts brotli -->
            <add input="{HTTP_ACCEPT_ENCODING}" pattern="br" negate="false" />
            <!-- pre-compressed brotli file exists -->
            <add input="{REQUEST_FILENAME}.br" matchType="IsFile" negate="false" />
          </conditions>
          <!-- serve pre-compressed file -->
          <action type="Rewrite" url="{R:1}{R:2}.{R:3}.br{R:4}" />
        </rule>
        <rule name="ServerPreCompressedZopfli" stopProcessing="true">
          <match url="^(.*/)?(.*?)\.(css|js)([?#].*)?$" />
          <conditions>
            <!-- client accepts gzip -->
            <add input="{HTTP_ACCEPT_ENCODING}" pattern="gzip" negate="false" />
            <!-- pre-compressed zopfli file exists -->
            <add input="{REQUEST_FILENAME}.gz" matchType="IsFile" negate="false" />
          </conditions>
          <!-- serve pre-compressed file -->
          <action type="Rewrite" url="{R:1}{R:2}.{R:3}.gz{R:4}" />
        </rule>
      </rules>
      <outboundRules>
        <!-- restore the correct mime type -->
        <rule name="RestoreMime" enabled="true">
          <match serverVariable="RESPONSE_Content_Type" pattern=".*" />
          <conditions>
            <add input="{HTTP_URL}" pattern="\.((?:css|js)\.(gz|br))" />
            <add input="{CompressedExtensions:{C:1}}" pattern="(.+)" />
          </conditions>
          <action type="Rewrite" value="{C:3}" />
        </rule>
        <rule name="RemoveRangeBrotli" preCondition="PreCompressedBrotli" enabled="false">
          <match serverVariable="RESPONSE_Content_Range" pattern=".*" />
          <action type="Rewrite" value="" />
        </rule>
        <rule name="RemoveRangeZopfli" preCondition="PreCompressedZopfli" enabled="false">
          <match serverVariable="RESPONSE_Content_Range" pattern=".*" />
          <action type="Rewrite" value="" />
        </rule>
        <!-- indicate response is encoded with brotli -->
        <rule name="AddEncodingBrotli" preCondition="PreCompressedBrotli" enabled="true" stopProcessing="true">
          <match serverVariable="RESPONSE_Content_Encoding" pattern=".*" />
          <action type="Rewrite" value="br" />
        </rule>
        <!-- indicate response is encoded with gzip -->
        <rule name="AddEncodingZopfli" preCondition="PreCompressedZopfli" enabled="true" stopProcessing="true">
          <match serverVariable="RESPONSE_Content_Encoding" pattern=".*" />
          <action type="Rewrite" value="gzip" />
        </rule>
        <preConditions>
          <preCondition name="PreCompressedZopfli">
            <add input="{HTTP_URL}" pattern="\.((?:css|js)\.gz)" />
          </preCondition>
          <preCondition name="PreCompressedBrotli">
            <add input="{HTTP_URL}" pattern="\.((?:css|js)\.br)" />
          </preCondition>
        </preConditions>
      </outboundRules>
    </rewrite>
  </system.webServer>
</configuration>