use spring security oauth2 resource owner password scheme as authentication provider

gistfile1.java

public class ResourceOwnerAuthenticationProvider implements AuthenticationProvider {

    private String apiEndpoint;
    private String clientId;
    private String accessTokenUri;
    private String clientSecret;
    private List<String> scope;

    @Override
    public boolean supports(Class<?> authentication) {
        return authentication.equals(UsernamePasswordAuthenticationToken.class);
    }

    @Override
    public Authentication authenticate(Authentication authentication) throws AuthenticationException {

        String username = (String) authentication.getPrincipal();
        String password = (String) authentication.getCredentials();
        ResourceOwnerPasswordResourceDetails resourceDetails = createResourceDetails(username, password);
        OAuth2RestTemplate restTemplate = new OAuth2RestTemplate(resourceDetails);
        Client client = new Client(apiEndpoint, restTemplate);

        UserData userData = null;
        try {
            userData = client.selectUser();
        } catch (HttpClientErrorException e) {
            if (HttpStatus.UNAUTHORIZED.equals(e.getStatusCode())) {
                throw new BadCredentialsException("invalid login", e);
            }
        }

        if (userData != null) {
            UsernamePasswordAuthenticationToken authentication =
                    new UsernamePasswordAuthenticationToken(
                            userData.getEmail(),
                            null,
                            Arrays.asList(new SimpleGrantedAuthority("ROLE_USER")));
            authentication.setDetails(
                    new AuthenticationContext(
                            resourceDetails,
                            restTemplate.getOAuth2ClientContext()));
            return authentication;

        } else {
            throw new IllegalStateException(
                    "login seems to have been successful but I'm missing the respective user data!");
        }
    }

    private ResourceOwnerPasswordResourceDetails createResourceDetails(String username, String password) {
        ResourceOwnerPasswordResourceDetails resourceDetails = new ResourceOwnerPasswordResourceDetails();
        resourceDetails.setAccessTokenUri(accessTokenUri);
        resourceDetails.setClientId(clientId);
        resourceDetails.setClientSecret(clientSecret);
        resourceDetails.setScope(scope);
        resourceDetails.setUsername(username);
        resourceDetails.setPassword(password);
        return resourceDetails;
    }

    public void setAPIEndpoint(String apiEndpoint) {
        this.apiEndpoint = apiEndpoint;
    }

    public void setClientId(String clientId) {
        this.clientId = clientId;
    }

    public void setAccessTokenUri(String accessTokenUri) {
        this.accessTokenUri = accessTokenUri;
    }

    public void setClientSecret(String clientSecret) {
        this.clientSecret = clientSecret;
    }

    public void setScope(List<String> scope) {
        this.scope = scope;
    }

}

Hey! Thanks for that! What is this Client class?

I guess it's something like UserDetailsService or something that does a call to "/userinfo" endpoint. But seems a userData response only contains email as principal.