feat: Add Decision Record for token refresh

docs/development/decision-records/2024-03-05_token_refresh/README.md

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+# Tractus-X Token Refresh
+
+## Decision
+
+Implement token refresh for the Tractus-X EDC Data Plane according to the [Tractus-X Refresh Token Grant Profile](https://github.com/eclipse-tractusx/tractusx-profiles/blob/main/tx/refresh/refresh.token.grant.profile.md).
+This enables provider data planes to implement refresh tokens in an interoperable way for client applications using the
+Tractus-X EDC Connector.
+
+Note refresh token support will be done almost exclusively in Tractus-X EDC, except for a few minor updates to upstream
+EDC.
+
+## Rationale
+
+Data providers may use short-lived tokens for HTTP client pull data transfers to enhance security. Refresh tokens allow
+data access to be maintained using short-lived tokens without starting a new transfer process.
+
+## Approach
+
+The upstream EDC `DefaultDataPlaneAccessTokenServiceImpl` will be replaced to create a refresh token pinned to the
+client's DID. This TX implementation will use the following upstream EDC enhancements:
+
+- An upstream EDC decorator that adds the client DID as an extension property to the signaling request.
+- Upgrade the `AccessTokenData` type to allow for extensible properties to enable the `AccessTokenDataStore` to persist
+  the renewal token.
+
+Tractus-X EDC will implement token refresh based on
+the [Trasctus-X Refresh Token Grant Profile](https://github.com/eclipse-tractusx/tractusx-profiles/blob/main/tx/refresh/refresh.token.grant.profile.md)
+
+### Provider Data Plane
+
+#### TX DataPlaneAccessTokenService
+
+An implementation of the `DataPlaneAccessTokenService` will be provided that overrides the
+default `DefaultDataPlaneAccessTokenServiceImpl` implementation. The TX implementation will do the following:
+
+- Create an expiring access token and set the `expiresIn` attribute of the `DataAddress.`
+- Create a refresh token that is returned in the `refreshToken` property of the `DataAddress`.
+- Provide a configuration option to set the `refreshEndpoint` property of the `DataAddress.` If not set,
+  the `refreshEndpoint` property will not be included.
+
+It will be possible for distributions not to include the TX implementation of the `DataPlaneAccessTokenService` and
+substitute another or revert to the EDC default implementation.
+
+The refresh token will be sender-constrained to the client DID passed as part of the `DataFlowStartMessage`.
+
+#### OAuth 2 Refresh API
+
+The provider data plane will be extended to add a public API that implements the OAuth2 `refresh_token` grant. The
+refresh token will be verified according to the steps laid out in the _Tractus-X Refresh Token Grant Profile._ When a
+refresh request is successfully made, a new access token and refresh token will be generated and returned to the client.
+If a refresh token request fails due to a validation error, the associated access token and refresh token will be
+invalidated.
+
+### Client-side Token Refresh
+
+A client will be able to initiate a token refresh request in three ways:
+
+- Request data through a client data plane instance, which will check the token expiration and issue a refresh request
+  if required. This behavior will be transparent to the client.
+- Request data directly and check if the access token is expired. If the token is expired, the client can call a client
+  data plane management API to renew the access token.
+- Request data directly and handle access token renewal using OAuth 2 directly.
+
+To support refresh token renewal, a DIM specific extension will be added that requests the authentication JWT to be
+signed using a key managed by DIM. This extension can use the same DIM API as the IATP extension.  
+