Cloudera Manager Installation Problem (Oracle SDK)

Hey everybody,

I try to install the cloudera manager via the manager installer but everytime i run it, i get the following error:

Reading package lists…
Building dependency tree…
Reading state information…
The following NEW packages will be installed:
oracle-j2sdk1.7
0 upgraded, 1 newly installed, 0 to remove and 56 not upgraded.
Need to get 142 MB of archives.
After this operation, 292 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
oracle-j2sdk1.7
E: There were unauthenticated packages and -y was used without --allow-unauthenticated

I am using Ubuntu Xenial 16.04 LTS.
Can anybody help me?

Thank you very much in advance!