fails to download keyring for REPOSITORY_EXTRA_KEYS

[youam]

on my newly created buildhost running debian jessie, installed with the automatic script, there's no curl. this seems to be a dependency when using the REPOSITORY_EXTRA_KEYS setting:

+ IFS=,
+ read -a array
+ for key in '"${array[@]}"'
+ curl -O http://debian.youam.de/youam.gpg
/usr/bin/build-and-provide-package: line 683: curl: command not found
+ gpg --no-default-keyring --keyring /tmp/apt-25802/keyring.gpg --import youam.gpg
gpg: keyring `/tmp/apt-25802/keyring.gpg' created
gpg: can't open `youam.gpg': No such file or directory
gpg: Total number processed: 0
+ unset key
...

it then goes on trying to build, but the packages in the REPOSITORY_EXTRA stay untrusted, and so the buld fails