You may start thinking to Federate Server with Portal.
When you federate a server with your portal, the portal's security store controls all access to the server. This provides a convenient sign-on experience, but also impacts how you access and administer the federated server.
In order to save credentials, you need to add the service as an item under My Content. When you enter the service url, you should be prompted to enter credentials and see a radio button to select to save the credentials. There are a few scenarios where you will not see the option to save the credentials:
1. If the service is secured with web-tier authentication (IWA, PKI, Basic, etc.), you won't be able to save credentials.
2. If the service is inaccessible by Portal (ex blocked by a firewall or proxy configuration), you won't be able to save credentials.
3. If Portal does not trust the SSL certificate used by the Server web adaptor, you won't be able to save credentials.
Once the item has been saved, you'll add the item to the web map rather than the service url and you should not be prompted for credentials.
Did you ever get an answer to this? I think we have a secured service that a user added with stored credentials and now the password has changed and it keeps blocking the user from signing in...
If we could find the item we would change it here... That is the problem. The user has a bunch of content on both Portal and AGOL across 4 ArcGIS Servers and doesn't recall ever adding a service with cached credentials. Is there a report or something that we could run to "find" that service?
So where is our user blocked ("keeps blocking the user from signing in...") and is prompted for sign in? That web map or web application should be able to tells us which service is unable to load due to lack of credentials?