One thing that I found lacking in the SimpleLogin API is that, it doesn't expose an API endpoint to create a contact based on the alias' email address. Rather, the POST /api/aliases/:alias_id/contacts endpoint requires the alias ID. So, I ended up downloading all aliases as multiple batches (each query returns upto 20 results) and saved them as json files in a folder.
With them in a folder, I could use jq to parse all of these json files for an alias email address, get its ID and further use it to create a new contact. All of this works like a charm now. My entire process works independent of the dashboard now: create a new alias, get its ID, create a contact, copy the reverse contact address, paste it on my email client.
The first part for getting the alias ID involves this command:
cat ~/Documents/SimpleLoginFiles/* | jq '.aliases[] | select(.email=="aliasAddress")' | jq '.id' | tr -d '\n' | pbcopy .
It was a pleasant surprise when I learned that I could pipe in all files in a folder to jq, instead of having to implement some sort of a loop logic. I don't know if it's bash's magic or something that jq handles elegantly.
The second part for creating the contact involves this command:
curl --location --request POST 'https://app.simplelogin.io/api/aliases/aliasID/contacts' --header 'Authentication: token' --header 'Content-Type: application/json' --data-raw '{"contact": "contactAddress"}' | jq '.reverse_alias' | tr -d "\\"" | pbcopy .
If you are wondering what the tr -d "\\"" part is, it's to remove the unwanted escape characters that appears as a part of the SimpleLogin API output. I imagine it's possible to remove that using jq, but for now, the current workaround is sufficient.
The contact's reverse address is finally in my clipboard, which I can paste on Apple Mail:
Reverse alias on the "To" field of the composer
SimpleLogin recently announced an update to their Firefox extension too, to create reverse aliases (contact reverse address) on the go, but I like this API-based process better. The extension takes a while to populate all aliases.