Separate Staging and Dev Constants

[okis-netlight]

Description

Since we are working with dev, staging, and production environments, we should update our codebase to support using different constants (urls and CORS policies, etc) when we are in a staging environment. Currently the staging and dev environments use the same set of constants, so this issue would involve separating those into different sets.

Tasks

• Set CORS policies for staging environment
• Take NODE_ENV=='staging' into consideration when setting constants such as URLs