web.config redirect non-www to www

Question

I need to redirect non-www URLs to www URL for both HTTP and HTTPS URLs. I tried following rules in web.config.

<rule name="Redirect to WWW" stopProcessing="true">
    <match url=".*" />
    <conditions>
        <add input="{HTTP_HOST}" pattern="^example.com$" />
    </conditions>
    <action type="Redirect" url="http://www.example.com/{R:0}" redirectType="Permanent" />
</rule>

<rule name="Redirect to WWW https" stopProcessing="true">
    <match url=".*" />
    <conditions>
        <add input="{HTTPS}" pattern="^example.com$" />
    </conditions>
    <action type="Redirect" url="https://www.example.com/{R:0}" redirectType="Permanent" />
</rule>

It works perfectly for non-ssl URL but in case of SSL it redirect from https://example.com to http://www.example.com.

Answer 1

For a safer rule that works for both Match Any and Match All situations, you can use the Rewrite Map solution. It’s a perfectly good solution with the only drawback being the ever so slight extra effort to set it up since you need to create a rewrite map before you create the rule. In other words, if you choose to use this as your sole method of handling the protocol, you’ll be safe.

You can create a Rewrite Map called MapProtocol, you can use {MapProtocol:{HTTPS}} for the protocol within any rule action.

<rewrite>
  <rules>
    <rule name="Redirect to www" stopProcessing="true">
      <match url="(.*)" />
      <conditions trackAllCaptures="false">
        <add input="{HTTP_HOST}" pattern="^example.com$" />
      </conditions>
      <action type="Redirect"
        url="{MapProtocol:{HTTPS}}://www.example.com/{R:1}" />
    </rule>
  </rules>
  <rewriteMaps>
    <rewriteMap name="MapProtocol">
      <add key="on" value="https" />
      <add key="off" value="http" />
    </rewriteMap>
  </rewriteMaps>
</rewrite>

Reference