Deprecated GitLab CI API clean up - README

doc/ci/api/README.md

 # GitLab CI API
 
+## Purpose
+
+Main purpose of GitLab CI API is to provide necessary data and context for
+GitLab CI Runners.
+
+For consumer API take a look at this [documentation](../../api/README.md) where
+you will find all relevant information.
+
 ## Resources
 
-- [Projects](projects.md)
 - [Runners](runners.md)
 - [Commits](commits.md)
 - [Builds](builds.md)
-
-
-## Authentication
-
-GitLab CI API uses different types of authentication depends on what API you use.
-Each API document has section with information about authentication you need to use.
-
-GitLab CI API has 4 authentication methods:
-
-* GitLab user token & GitLab url
-* GitLab CI project token
-* GitLab CI runners registration token
-* GitLab CI runner token
-
-
-### Authentication #1: GitLab user token & GitLab url
-
-Authentication is done by
-sending the `private-token` of a valid user and the `url` of an
-authorized GitLab instance via a query string along with the API
-request:
-
-    GET http://gitlab.example.com/ci/api/v1/projects?private_token=QVy1PB7sTxfy4pqfZM1U&url=http://demo.gitlab.com/
-
-If preferred, you may instead send the `private-token` as a header in
-your request:
-
-    curl --header "PRIVATE-TOKEN: QVy1PB7sTxfy4pqfZM1U" "http://gitlab.example.com/ci/api/v1/projects?url=http://demo.gitlab.com/"
-
-
-### Authentication #2: GitLab CI project token
-
-Each project in GitLab CI has it own token. 
-It can be used to get project commits and builds information.
-You can use project token only for certain project.
-
-### Authentication #3: GitLab CI runners registration token
-
-This token is not persisted and is generated on each application start.
-It can be used only for registering new runners in system. You can find it on 
-GitLab CI Runners web page https://gitlab-ci.example.com/admin/runners
-
-### Authentication #4: GitLab CI runner token
-
-Every GitLab CI runner has it own token that allow it to receive and update 
-GitLab CI builds. This token exists of internal purposes and should be used only 
-by runners
-
-## JSON
-
-All API requests are serialized using JSON.  You don't need to specify
-`.json` at the end of API URL.
-
-## Status codes
-
-The API is designed to return different status codes according to context and action. In this way if a request results in an error the caller is able to get insight into what went wrong, e.g. status code `400 Bad Request` is returned if a required attribute is missing from the request. The following list gives an overview of how the API functions generally behave.
-
-API request types:
-
-- `GET` requests access one or more resources and return the result as JSON
-- `POST` requests return `201 Created` if the resource is successfully created and return the newly created resource as JSON
-- `GET`, `PUT` and `DELETE` return `200 OK` if the resource is accessed, modified or deleted successfully, the (modified) result is returned as JSON
-- `DELETE` requests are designed to be idempotent, meaning a request a resource still returns `200 OK` even it was deleted before or is not available. The reasoning behind it is the user is not really interested if the resource existed before or not.
-
-The following list shows the possible return codes for API requests.
-
-Return values:
-
-- `200 OK` - The `GET`, `PUT` or `DELETE` request was successful, the resource(s) itself is returned as JSON
-- `201 Created` - The `POST` request was successful and the resource is returned as JSON
-- `400 Bad Request` - A required attribute of the API request is missing, e.g. the title of an issue is not given
-- `401 Unauthorized` - The user is not authenticated, a valid user token is necessary, see above
-- `403 Forbidden` - The request is not allowed, e.g. the user is not allowed to delete a project
-- `404 Not Found` - A resource could not be accessed, e.g. an ID for a resource could not be found
-- `405 Method Not Allowed` - The request is not supported
-- `409 Conflict` - A conflicting resource already exists, e.g. creating a project with a name that already exists
-- `422 Unprocessable` - The entity could not be processed
-- `500 Server Error` - While handling the request something went wrong on the server side