Give secret params a .value() method

[jhuleatt]

Description

Fixes #1264

Code sample

const functions = require('firebase-functions');
const { defineSecret } = require('firebase-functions/params');
const discordApiKey = defineSecret('DISCORD_API_KEY');

export const postToDiscord = functions.runWith({ secrets: [discordApiKey] }).https.onRequest(
  (req, res) => {
    const apiKey = discordApiKey.value();
    //…

https://firebase.google.com/docs/functions/config-env#secret_parameters

[taeold]

Can we add a changelog? I think this is a bugfix.

[jhuleatt]

Thanks, I added a changelog!

A couple of questions:

1. Do we need to add any guards to prevent this param type from being used outside of runtime, since secret values are only available to the function at runtime? Or does not inheriting from Parameter solve this for us?
2. Should the .value function throw an error if the secret value isn't available to the function (for example, if a developer forgot to add the secrets config array to the function)?

[Berlioz]

Other than one nit, LGTM.

[Berlioz]

couldn't someone deliberately set a secret to the empty string, which is falsy?

[jhuleatt]

Changed from a falsy check to val === undefined

[Berlioz]

LGTM