gistfile1.java

@Path("authenticate")
@Produces(MediaType.APPLICATION_JSON)
public class AuthResource {
    private final UserDAO userDAO;

    public AuthResource(UserDAO userDAO) {
        this.userDAO = userDAO;
    }

    @GET
    public User authenticate(@Context HttpContext context) {
        final String apiKey = getApiKeyFromAuthorizationHeader(context);
        final User user = userDAO.getUserByApiKey(apiKey);
        return user;
    }

    private String getApiKeyFromAuthorizationHeader(HttpContext context) {
        final String authorization = context.getRequest().getHeaderValue("Authorization");
        if (Strings.isNullOrEmpty(authorization)) {
            throw new WebApplicationException(Response.status(BAD_REQUEST).entity("Missing auth header").build());
        }
        final String[] pieces = authorization.split(" ");
        if (pieces.length != 2) {
            throw new WebApplicationException(Response.status(BAD_REQUEST).entity("Bad auth header").build());
        }
        if ("Basic".equals(pieces[0])) {
            return new String(Base64.decodeBase64(pieces[1]), Charsets.UTF_8);
        }
        return pieces[1];
    }
}