Getting HTTP error 404 accessing Hue via Knox

Support Question

How to solve the following issue?

We run CDP 7.1.7 SP2 CHF 18.
We followed Cloudera's description "CDP 7.1.7 / Authenticating Hue users with Knox SSO".

- The details given below are redacted -

Issue

With a newly started browser Knox was called, having no Cookies cached.

When connecting the service Hue a second time by clicking the appropriate icon in Knox, it works fine. The URL https://knox.mydomain.com/gateway/Business/hue/hue/editor/?type=impala is used.

The first connection to Hue via Knox fails, and the browser calls the URL https://knox.mydomain.com/gateway/Business/hue/%3FdoAs%3Duserid.

We get an HTTP error 404 (Page not found) with following details:

followed by the message

Configuration

Excerpt of XML configuration file of the default topology (we called it "Business.xml"):

<?xml version="1.0" encoding="utf-8"?>
<!--==============================================-->
<!-- DO NOT EDIT. This is an auto-generated file. -->
<!--==============================================-->
<topology>
    <generated>true</generated>
    <gateway>
        <provider>
            <role>federation</role>
            <name>SSOCookieProvider</name>
            <enabled>true</enabled>
            <param>
                <name>sso.authentication.provider.url</name>
                <value>https://knox_host.mydomain.com:8443/gateway/knoxsso/api/v1/websso</value>
            </param>
        </provider>
        <provider>
            <role>identity-assertion</role>
            <name>HadoopGroupProvider</name>
            <enabled>true</enabled>
            <param>
                <name>CENTRAL_GROUP_CONFIG_PREFIX</name>
                <value>gateway.group.config.</value>
            </param>
        </provider>
        <provider>
            <role>authorization</role>
            <name>XASecurePDPKnox</name>
            <enabled>true</enabled>
        </provider>
        <provider>
            <role>ha</role>
            <name>HaProvider</name>
            <enabled>true</enabled>
<!-- ... -->
           <param>
                <name>HUE</name>
                <value>enabled=true;maxFailoverAttempts=3;failoverSleep=1000;maxRetryAttempts=300;retrySleep=1000</value>
            </param>
<!-- ... -->
       </provider>
    </gateway>

    <service>
        <role>HUE</role>
        <url>https://hue_loadbalancer_host.mydomain.com:8888</url>
        <param>
            <name>httpclient.connectionTimeout</name>
            <value>5m</value>
        </param>
        <param>
            <name>httpclient.socketTimeout</name>
            <value>5m</value>
        </param>
    </service>
<!-- ... -->
</topology>