详解OAuth2 Token 一定要放在请求头中吗

public class OAuth2AuthenticationProcessingFilter{
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException,
			ServletException {
		try {
			// 1. 根据用户请求解析令牌，组装预登陆对象
			Authentication authentication = tokenExtractor.extract(request);
			if (authentication == null) {
				// 若是预登陆状态为空，把无状态登录清空
				if (stateless && isAuthenticated()) {
					SecurityContextHolder.clearContext();
				}
			}
			else {
				// 2. 根据token 来做真正的认证登录 Provier
				Authentication authResult = authenticationManager.authenticate(authentication);

				// 3. 登录成功逻辑
				eventPublisher.publishAuthenticationSuccess(authResult);
				SecurityContextHolder.getContext().setAuthentication(authResult);
			}
		}
		catch (OAuth2Exception failed) {
      // 异常通知逻辑 Spring Event
			...
			return;
		}
		chain.doFilter(request, response);
	}
}

public class BearerTokenExtractor implements TokenExtractor {
	@Override
	public Authentication extract(HttpServletRequest request) {
		// 1. 解析token
		String tokenValue = extractToken(request);
		if (tokenValue != null) {
			// 2. 创建一个authentication 返回
			PreAuthenticatedAuthenticationToken authentication = new PreAuthenticatedAuthenticationToken(tokenValue, "");
			return authentication;
		}
		return null;
	}

	protected String extractToken(HttpServletRequest request) {
		// 1.1 优先从请求header 获取token
		String token = extractHeaderToken(request);
		// 1.2 若是请求token 中没有，则获取请求参数中的 access_token 参数
		if (token == null) {
			token = request.getParameter(OAuth2AccessToken.ACCESS_TOKEN);
		}
		return token;
	}
}