No, App Platform does not currently support injecting values as files on disk. However, you can add the contents of a certificate or file as an environment variable and then save that value to disk using build or run time commands.
For example, MongoDB requires a Certificate Authority (CA) certificate for clients to connect to a cluster, and most MongoDB clients require the certificate to be a file on disk. You can work around the injection limitation by creating an environment variable, such as MONGO_CA_CERT=${db.CA_CERT}, during the app’s creation process or by updating its settings. Then, you can add a command to the app that creates the certificate file upon runtime, such as echo $MONGO_CA_CERT > ca_cert.cert && <original run command>. App Platform requires the original run time command to start the app upon runtime.