<p>We have a running TYPO3 9.5.7 System on a kubernetes Cluster. TYPO3 runs on a docker container with PHP7.3-apache. The complete site has an SSL (Let's Encrypt) certificate. I can load the TYPO3 Backend. Now, if I try to activate an extension with the extensionmanager I got the following error:</p>

<p><code>Mixed Content: The page at 'https://my.domain.com/typo3/index.php?route=%2Fmain&amp;token=b264e888080675e401a2a6162a9e7be22f968b7e' was loaded over HTTPS, but requested an insecure resource 'http://my.domain.com/typo3/index.php?route=%2Ftools%2FExtensionmanagerExtensionmanager%2F&amp;token=8ab8e4a2eef2832bf7ff4615b9787642cadc6e01&amp;tx_extensionmanager_tools_extensionmanagerextensionmanager%5BextensionKey%5D=of_customisation&amp;tx_extensionmanager_tools_extensionmanagerextensionmanager%5Baction%5D=unresolvedDependencies&amp;tx_extensionmanager_tools_extensionmanagerextensionmanager%5Bcontroller%5D=List'. This request has been blocked; the content must be served over HTTPS.</code></p>

<p>Has anyone an idea what I have to do to get rid of this error?</p>

<p>Thanks in advance</p>

<p>You should let TYPO3 know that it <a href="https://moc.net/om-moc/aktuelt/blogs/tech/running-typo3-cms-behind-https-proxy" rel="nofollow noreferrer">runs behind a HTTPS reverse proxy</a> in your <code>LocalConfiguration.php</code>:</p>

<pre class="lang-php prettyprint-override"><code>'SYS' =&gt; [
    'reverseProxyIP' =&gt; 'THE IP OF YOUR PROXY SERVER',
    'reverseProxyHeaderMultiValue' =&gt; 'last',
    'reverseProxySSL' =&gt; '*',
],
</code></pre>

<p>See the list of options on this topic <a href="https://github.com/TYPO3/TYPO3.CMS/blob/71cb708d764eba2614608558e85f4a7dc31fee47/typo3/sysext/core/Configuration/DefaultConfigurationDescription.yaml#L151-L169" rel="nofollow noreferrer">in the TYPO3 source</a>:</p>

<ul>
<li><code>reverseProxyIP</code>: List of IP addresses. If TYPO3 is behind one or more (intransparent) reverse proxies the IP addresses must be added here.</li>
<li><code>reverseProxyHeaderMultiValue</code>: Defines which values of a proxy header (eg HTTP_X_FORWARDED_FOR) to use, if more than one is found.</li>
<li><code>reverseProxyPrefix</code>: Optional prefix to be added to the internal URL (SCRIPT_NAME and REQUEST_URI).</li>
<li><code>reverseProxySSL</code>: <code>'*'</code> or list of IP addresses of proxies that use SSL (https) for the connection to the client, but an unencrypted connection (http) to the server. If <code>'*'</code> all proxies defined in <code>[SYS][reverseProxyIP]</code> use SSL.</li>
<li><code>reverseProxyPrefixSSL</code>: Prefix to be added to the internal URL (SCRIPT_NAME and REQUEST_URI) when accessing the server via an SSL proxy. This setting overrides <code>[SYS][reverseProxyPrefix]</code>.</li>
</ul>
