Authenticate OAuth Provider

curl --request POST \
  --url https://api.example.com/orgs/{org_id}/connections/oauth/validate \
  --header 'Content-Type: application/json' \
  --data '
{
  "type": "SLACK",
  "validation_url": "<string>",
  "subdomain": "<string>"
}
'

{
  "config": {
    "type": "OAUTH",
    "access_token": "<string>",
    "refresh_token": "<string>",
    "expires_in": 1,
    "next_refresh_at": 123,
    "scope": "<string>",
    "api_url": "<string>",
    "subdomain": "<string>"
  },
  "user": {
    "external_id": "<string>",
    "external_name": "<string>"
  }
}