You didn't say which release of Ambari server you're interested in, so I strongly recommend that you first consult the Cloudera Support Matrix on Cloudera's website, to confirm that your desired version of Ambari server is actually available for the release of RHEL you are targeting. The Ambari project at Apache might have different OS support levels available, although you should be aware that the Ambari project was retired in January of this year.
As far as access to the repository you mentioned, last year Cloudera changed their download policy and now to download Ambari binaries from Cloudera's private repository, you need a valid subscription. Please see and carefully read the announcement here: Transition to private repositories for CDH, HDP and HDF.
Toward the end of that announcement, you will see a section subtitled Ambari 2.7.x.x and HDP 3.x.x.x. You should follow the appropriate hyperlink underneath that and then carefully read the documentation. Note that the credentials to access the private repository where Cloudera is now distributing releases of Ambari are not generally the same ones to access Cloudera's website or the Cloudera community.
Bill Brooks, Community Moderator
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