I got a new Macbook Pro and I made a provisioning profile for my new app,
which I added to Organizer, and then downloaded the certificate.
However, the .cer file does not seem to get added to keychain access’s login key,
which results in not being able to choose the provisioning profile on xcode…
What could’ve gone wrong?
I assume that you created the certificate using your old Mac.
In that case, the private key is still stored on your old machine. It was automatically created when you created the CSR which was used to make your current certificate and never sent to Apple. The .cer you download only contains the public key.
You need both for signing purposes.
To solve this problem, either import your private key from your old mac or create a new developer certificate (follow the steps outlined in the provisioning portal of creating and submitting a csr). Be aware that the second option will invalidate your old certificate as only one certificate is allowed per developer.