Authenticate processes an authenticate request.

Request

• Base URL
  https://etcd.io (the document declares no server; this is the origin it was published from)
• Auth
  API key in header Authorization
• TypeScript
  https://skmtc.dev/etcd/apis/api-etcdserverpb-rpc-proto/docs/v3/auth/authenticate/post.ts

  A function with typed inputs. Its response is checked against the schema.