The main thing to consider is that since cloud instances are ephemeral and
untrusted, you won’t be leaving your credentials like your Play Store service
account JSON or your iTunes distribution certificate on the server.

Continuous Integration (CI) systems generally support encrypted environment 
variables to store private data. You can pass these environment variables 
using --dart-define MY_VAR=MY_VALUE while building the app.

Take precaution not to re-echo those variable values back onto the console in
your test scripts. Those variables are also not available in pull requests
until they’re merged to ensure that malicious actors cannot create a pull
request that prints these secrets out. Be careful with interactions with these
secrets in pull requests that you accept and merge.