Refresh Tokens in OpenID Connect
OpenID Connect Core 1.0 - Using Refresh Tokens (openid.net)
A Refresh Token is a credential defined by the OAuth 2.0 authorization framework (RFC 6749) (rfc-editor.org) that a client uses to obtain new Access Tokens when the current ones expire, or to obtain additional access tokens, without user re-authentication.
OIDC reuses the OAuth 2.0 Refresh Token Grant flow: a client sends the refresh token with grant_type=refresh_token to the Token Endpoint to receive a new access token.
OAuth 2.0 is an authorization protocol, focusing on granting delegated access to resources. OpenID Connect (OIDC) is an identity layer built on top of OAuth 2.0 to provide authentication and identity information (claims) about an End-User. OpenID Connect re-uses concepts specified by the OAuth 2.0 protocol and related standards.
ID Token as part of the Refresh Token Grant
The key addition in OIDC regarding refresh tokens is that the successful response from the Token Endpoint MUST also include a new ID Token if the openid scope was granted when the refresh token was issued.
This new ID Token provides up-to-date claims about the authentication event.
OIDC also defines the offline_access scope which a client must request during the initial authorization to signal its intent to use the refresh token for accessing resources when the user is not actively present.