Here’s a quick tip. You can set all the env vars in your .env file in Heroku with this.

cat .env | xargs heroku config:set

Want more proof, with actual fake passwords?!

~/heroku-thing$ cat .env | xargs heroku config:set
Setting ARCHIVE, AWS_ACCESS_KEY, AWS_SECRET_ACCESS_KEY, EVENTS_TABLE, PGPASSWORD, REDSHIFT_CONNECTION_STRING, SCHEMA_PATH, SOURCE, STAGING and restarting ⬢ heroku-thing-app... done, v5
ARCHIVE:                    s3://blah/archive/
AWS_ACCESS_KEY:             BOOP
AWS_SECRET_ACCESS_KEY:      BEEP
EVENTS_TABLE:               some_table
PGPASSWORD:                 correcthorsebatterystaple
REDSHIFT_CONNECTION_STRING: postgresql://blah@bloo:1111/foo
SCHEMA_PATH:                s3://schema.json
SOURCE:                     s3://blah/source/
STAGING:                    s3://blah/staging/