can I include user information while issuing an access token?

Together with:

@Bean
public TokenEnhancer tokenEnhancer() {
   return new CustomTokenEnhancer();
}

You have to include

@Bean
public DefaultAccessTokenConverter accessTokenConverter() {
    return new DefaultAccessTokenConverter();
}

and add everything to endpoints config:

@Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {

        endpoints
                .tokenStore(tokenStore)
                .tokenEnhancer(tokenEnhancer())
                .accessTokenConverter(accessTokenConverter())
                .authorizationCodeServices(codeServices)
                .authenticationManager(authenticationManager)
        ;
    }

Without it, your CustomTokenEnhancer will not work.

You will need to implement a custom TokenEnhancer like so:

public class CustomTokenEnhancer implements TokenEnhancer {

    @Override
    public OAuth2AccessToken enhance(OAuth2AccessToken accessToken, OAuth2Authentication authentication) {
        User user = (User) authentication.getPrincipal();
        final Map<String, Object> additionalInfo = new HashMap<>();

        additionalInfo.put("customInfo", "some_stuff_here");
        additionalInfo.put("authorities", user.getAuthorities());

        ((DefaultOAuth2AccessToken) accessToken).setAdditionalInformation(additionalInfo);

        return accessToken;
    }

}

and add it to your AuthorizationServerConfigurerAdapter as a bean with the corresponding setters

@Configuration
@EnableAuthorizationServer
protected static class AuthorizationServerConfiguration extends AuthorizationServerConfigurerAdapter {

    // Some autowired stuff here

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {
        // @formatter:off
        endpoints
            // ...
            .tokenEnhancer(tokenEnhancer());
        // @formatter:on
    }

    @Bean
    @Primary
    public AuthorizationServerTokenServices tokenServices() {
        DefaultTokenServices tokenServices = new DefaultTokenServices();
        // ...
        tokenServices.setTokenEnhancer(tokenEnhancer());
        return tokenServices;
    }

    // Some @Bean here like tokenStore

    @Bean
    public TokenEnhancer tokenEnhancer() {
        return new CustomTokenEnhancer();
    }

}

then in a controller (for example)

@RestController
public class MyController {

    @Autowired
    private AuthorizationServerTokenServices tokenServices;

    @RequestMapping(value = "/getSomething", method = RequestMethod.GET)
    public String getSection(OAuth2Authentication authentication) {
        Map<String, Object> additionalInfo = tokenServices.getAccessToken(authentication).getAdditionalInformation();

        String customInfo = (String) additionalInfo.get("customInfo");
        Collection<? extends GrantedAuthority> authorities = (Collection<? extends GrantedAuthority>) additionalInfo.get("authorities");

        // Play with authorities

        return customInfo;
    }

}

I'm personnaly using a JDBC TokenStore so my "Some autowired stuff here" are corresponding to some @Autowired Datasource, PasswordEncoder and what not.

Hope this helped!

If you are using Spring's JwtAccessTokenConverter or DefaultAccessTokenConverter you can add your custom CustomTokenEnhancer (see first response) and apply it using a TokenEnhancerChain like this:

@Override
public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {

    TokenEnhancerChain enhancerChain = new TokenEnhancerChain();
    enhancerChain.setTokenEnhancers(Arrays.asList(customTokenEnhancer(), accessTokenConverter()));

    endpoints.tokenStore(tokenStore())
            .tokenEnhancer(enhancerChain)
            .authenticationManager(authenticationManager);
}

@Bean
protected JwtAccessTokenConverter jwtTokenEnhancer() {
    JwtAccessTokenConverter converter = new JwtAccessTokenConverter();
    converter.setSigningKey("my_signing_key");
    return converter;
}

@Bean public TokenEnhancer customTokenEnhancer() {
    return new CustomTokenEnhancer();
}

Another solution is to create a custom TokenConverter that extends Spring's JwtAccessTokenConverter and override the enhance() method with your custom claims.

public class CustomTokenConverter extends JwtAccessTokenConverter {

@Override
public OAuth2AccessToken enhance(OAuth2AccessToken accessToken, OAuth2Authentication authentication) {

    final Map<String, Object> additionalInfo = new HashMap<>();
    additionalInfo.put("customized", "true");
    User user = (User) authentication.getPrincipal();
    additionalInfo.put("isAdmin", user.getAuthorities().stream().map(GrantedAuthority::getAuthority).collect(Collectors.toList()).contains("BASF_ADMIN"));
    ((DefaultOAuth2AccessToken) accessToken).setAdditionalInformation(additionalInfo);

    return super.enhance(accessToken, authentication);
    }
} 

And then:

@Override
public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {

    endpoints.tokenStore(tokenStore())
            .tokenEnhancer(customTokenEnhancer())
            .authenticationManager(authenticationManager);
}

@Bean public CustomTokenConverter customTokenEnhancer() {
    return new CustomTokenConverter();
}