** The new provider source attribute in Terraform 0.13 allows users to declare the registry source of a Terraform provider, creating a clear workflow for using providers from the Terraform Registry. This attribute is part of the required_providers setting inside a terraform configuration block and enables automatic download and installation of partner and community providers. The provider source string is made up of the hostname, namespace, and type, with optional hostname and namespace values that can be omitted or set to default values. Local names can be declared for multiple providers with the same type to easily identify them in the configuration. Third-party providers need to be assigned an arbitrary source and placed in a specific directory hierarchy for Terraform to find and use them. Users will need to upgrade their configurations by adding required_providers entries for non-HashiCorp-owned providers. The new feature aims to benefit Terraform users and provider developers alike, making it easier to include community and partner providers in the core terraform init workflow.