Allow to get the ACCESS_TOKEN from an environment variable

[aboglioli]

From #40

It allows to use environment variables to replace variables from .stdlib.
It's possible to set the ACCESS_TOKEN directly in an environment variable called ACCESS_TOKEN.

[wKovacs64]

Some thoughts on this:

1. Should the environment variable be called something more specific to avoid potential collisions? Perhaps STDLIB_ACCESS_TOKEN?
2. As it stands, this change will still require the .stdlib file to exist (it'll throw otherwise). Should the majority of the readCredentials function be wrapped in an if to skip reading the file if the environment variable is present?
3. Do we need another env variable correlating to the CREATED_AT key from .stdlib? Probably not, as it doesn't appear to be used anywhere other than when writing the file. Just curious.

[aboglioli]

That's correct! I thought in a .stdlib file without ACCESS_TOKEN, or with any random string but this solution could bring problems as you said.

I'm going to fix this. This was thought as a fast solution to deploy with any CI system.

Thanks for your review!

[aboglioli]

The only problem is: if in the future stdlib needs new data from new variables, they have to be added to the object returned inside the if (process.env.STDLIB_ACCESS_TOKEN) and check if they are present.

[keithwhor]

What I would do instead is something like this;

if (process.env.hasOwnProperty('STDLIB_ACCESS_TOKEN')) {
  let prefix = 'STDLIB_';
  return Object.keys(process.env)
    .filter(key => key.indexOf(prefix) === 0)
    .map(key => key.substr(prefix.length))
    .reduce((obj, key) => {
      obj[key] = process.env[prefix + key];
      return obj;
    }, {});
}

That way you can add more variables in the future if necessary. If you make this change I can merge it. :)

[aboglioli]

👍

[keithwhor]

I merged this, but we'll be updating the .stdlib usage soon. :)

[aboglioli]

Great! I think .stdlib file could be in user configuration (for example, /home/user/.config/stdlib/config_filein Linux). You don't have to care about this file in a public repository.

And overwriting the same configuration with environment variables.