$ sudo security add-generic-password -a uuu -s sss -w ppp -A /Library/Keychains/System.keychainThis did the trick, thanks. I'm still not sure why I couldn't just copy the keychain entry altool made to the system keychain; if I try it throws an "An error has occurred. Unable to add an item to the current keychain. One or more parameters passed to a function were not valid." error message.

While I'm sure the non-keychain options would work fine, I'd like to use the keychain if possible as it is is much more secure way to store the account password.--store-password-in-keychain-item is how I was attempting to add the item to my keychain. Interestingly, if I try to run this from the build server, I get no errors, but I also don't see any entry for it in the keychain app:Running as SYSTEMBuilding in workspace /Users/Shared/Jenkins/Home/workspace/CredentialTest[CredentialTest] $ /bin/sh -xe /Users/Shared/Jenkins/tmp/jenkins4349644463532595359.sh+ xcrun altool --store-password-in-keychain-item someItem -u some@email.com -p '123456'+ xcrun altool --notarization-info ab123123-123a-123a-123a-123abc123abc -u some@email.com -p @keychain:someItem2019-11-26 10:51:06.918 altool[5777:830527] *** Error: The keychain returned error code: -25291. Failed to get the password for the keychain item 'someItem'.If I login as the jenkins user and add the keychain item the same way, I get a success message that I don't see above ("Stored the password in the keychain item...", and I then see it in my local items keychain.I suspect this has to do with Jenkins being started as a LaunchDaemon.https://stackoverflow.com/questions/47582989/launchd-not-able-to-access-mac-os-keychainsHowever, SessionCreate is already set to true in /Library/LaunchDaemons/org.jenkins-ci.plist so I'm really not sure what the issue could be or how to troubleshoot further from here.