Arcgis Enterprise items ask me to sign in to local EC2 instance

[HansFelix]

I installed ArcGIS Enterprise, Portal and server works fine but when I tried to access items from portal folder I receive a warning saying to sign in to access the item. Did I miss some config?

[Scott_Tansley]

it looks like you're using a hostname in the 'web map':

   ec2amaz-4m3apc1

you would typically using a fully-qualified domain name there:

   ec2amaz-4m3apc1.domain.com

the fully qualified domain name is typically trusted whereas the hostname is not.  Have you got an alias to use?  That's a particularly gruesome URL otherwise.  I strongly recommend create an alias before you start loading any content.  e.g. mygis.domain.com.  

[A_Wyn_Jones]

Just to add to Scott's answer, if this is a new Enterprise and you've registered the web adaptor for Portal and Server - you may need to amend the web adaptors to use a friendly DNS alias on the registration page. Please see:

https://enterprise.arcgis.com/en/web-adaptor/latest/install/iis/configure-arcgis-web-adaptor-portal....