Spring Security OAuth2 token refreshed by WebClient but stored as "anonymousUser" - spring-boot

Question

I'm trying to implement Spring OAuth2 with WebClient saving refresh tokens for auto renewal in a JdbcOAuth2AuthorizedClientService.
When I first grant access with the Google prompt the token is stored perfectly as a row in the oauth2_authorized_client table for the principal_name that granted access, let's say john#gmail.com.
Later, when I want to use that stored access_token in a scheduled task (no user interaction) I can fetch it like this and inject it in my webClient:
private final OAuth2AuthorizedClientService authorizedClientService;
// ...
OAuth2AuthorizedClient authorizedClient = authorizedClientService.loadAuthorizedClient("google", "john#gmail.com");
return webClient.get()
.uri(CALENDAR_URL, uriBuilder ->
uriBuilder.path("/calendars/primary/events")
.queryParam("key", API_KEY)
.build())
.attributes(oauth2AuthorizedClient(authorizedClient))
.retrieve()
.bodyToMono(String.class);
This time the expired token gets automatically renewed (hurray!) but for some reason it is stored in the database table as a new row with principal_name as anonymousUser instead of john#gmail.com. Why is that?
This is my WebClient configuration:
#Bean
public OAuth2AuthorizedClientService oAuth2AuthorizedClientService(JdbcOperations jdbcOperations,
ClientRegistrationRepository clientRegistrationRepository) {
return new JdbcOAuth2AuthorizedClientService(jdbcOperations, clientRegistrationRepository);
}
#Bean
public WebClient webClient(ClientRegistrationRepository clientRegistrationRepository, OAuth2AuthorizedClientService authorizedClientService) {
AuthorizedClientServiceOAuth2AuthorizedClientManager manager = new AuthorizedClientServiceOAuth2AuthorizedClientManager(
clientRegistrationRepository, authorizedClientService);
manager.setAuthorizedClientProvider(new DelegatingOAuth2AuthorizedClientProvider(
new RefreshTokenOAuth2AuthorizedClientProvider(),
new ClientCredentialsOAuth2AuthorizedClientProvider()));
ServletOAuth2AuthorizedClientExchangeFilterFunction oauth2 = new ServletOAuth2AuthorizedClientExchangeFilterFunction(
manager);
oauth2.setDefaultClientRegistrationId("google");
return WebClient.builder()
.filter(oauth2)
.apply(oauth2.oauth2Configuration())
.build();
}