Handle Basic Auth enabled on Saleor instance

[witoszekdev]

What I'm trying to achieve

Saleor Cloud allows setting up Basic Auth authentication when setting up an environment: https://docs.saleor.io/cloud/restricting-api-access#api-password-protection

When installing apps in such Saleor instance it results in an error, because app cannot fetch app id when handling register request.

Describe a proposed solution

• App separate error message with explanation when we get HTTP 401 error with link to docs
• Allow configuration for Basic Auth, so that app can make authenticated requests