Is your feature request related to a problem? Please describe.
If there is DISABLE_USER_REGISTRATION in env no one should be able to do signup. By signup form or using github signup.

Describe the solution you'd like
If env has DISABLE_USER_REGISTRATION set to true, user should not be able to signup. We will restrict signup request from API side by adding check to DISABLE_USER_REGISTRATION env.

Like following condition we can put into,

    if (process.env.DISABLE_USER_REGISTRATION === 'true') throw new ApiException('Account creation is disabled');

• Same condition we can put at,

  impler.io/apps/api/src/app/auth/auth.controller.ts

  Line 46 in 27c620c

  githubAuth() {

  as well.
• We also have to put validator for it in,
  

  impler.io/apps/api/src/config/env-validator.ts

  Line 6 in 27c620c

  const validators: { [K in keyof any]: ValidatorSpec<any[K]> } = {

• To utilize it in self-hosted deployments we have to put it into docker-compose.yml file env for API at,
  

  impler.io/docker/docker-compose.yml

  Line 25 in 27c620c

  environment:

• Self-hosted deployments utilizes .env.example file envs which goes into,
  

  impler.io/docker/.env.example

  Line 4 in 27c620c

  ## General

Describe alternatives you've considered

Additional context