Document the REST API token-based security requirements for Zowe API services

[plavjanik]

• [x] Migrate guidance on Exposing Functions of ESM Microservice to REST API Callers to Zowe and update it so it is in conformance with current APIML implementation and ZAAS
  • Describes authentication from the perspective of the API client
    • Format of the responses when a client tries to access a protected endpoint without proper authentication (what are the expected headers and cookies for token-based authentication)
    • Format of accessing endpoints with HTTP basic authentication
    • Unified API to obtain a token from the REST API service
    • Format of accessing endpoints with the token
• [x] The requirements include:
  • Format of the responses when a client tries to access a protected endpoint without proper authentication
  • Format of accessing endpoints with HTTP basic authentication
  • Unified API to obtain a token from the REST API service
  • Format of accessing endpoints with the token