@blubberschwaetz,
Cloudera's lifecycle support policies are documented here:
https://www.cloudera.com/legal/policies/support-lifecycle-policy.html
Cloudera Enterprise 6.1 is supported until the end of December 2021, so yes an installation of CDH6.1.1 will quickly become an outdated, unmaintained platform and you should inform your customer of that fact if they are not aware of it already. You can find the most recent official reminder of the previous announcement that Cloudera Enterprise 6.x will be reaching End of Support (EoS) in 2021 here:
March 2021 Customer Advisory - 2: End of Support for Cloudera Products (CDH/CM 6.x & HDP 3.x)
I don't know that anyone at Cloudera can help you if you are struggling to get along with Cloudera's policies; those policies govern the use of Cloudera's software. If you are not a formal Cloudera partner and you do not have a valid subscription, no one at Cloudera will be able to give you credentials or "a download link to be used without credentials" to be able to access Cloudera's private repository in order to install CDH 6.1.1 on your premises. And that is true regardless of whether or not the resulting installed system would be used for testing third-party software or for production use.
If you're not willing to enter into a partnership agreement with Cloudera, your next most straightforward solution would be to acquire a Cloudera subscription yourself. You can get started toward that goal by contacting the Cloudera Sales Team to find out more about your subscription options.
Otherwise, no, I have no ideas on how who to solve your case.
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