signalr has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

这个错误通常是由于浏览器的同源策略导致的。同源策略是浏览器的一种安全机制，它限制了一个页面从另一个源加载任何资源。如果你的应用程序试图从不同的源加载资源，浏览器就会阻止这个请求，除非服务器在响应中包含了适当的 CORS 头信息。

要解决这个问题，你需要在服务器端配置 CORS 头信息。具体来说，你需要在响应头中添加一个名为 "Access-Control-Allow-Origin" 的头信息，并将其设置为允许访问的域名或 IP 地址。例如，如果你想允许所有域名访问你的资源，可以将该头信息设置为 "*":

Access-Control-Allow-Origin: *

如果你只想允许特定的域名或 IP 地址访问你的资源，可以将该头信息设置为相应的值。例如，如果你只想允许 example.com 访问你的资源，可以将该头信息设置为:

Access-Control-Allow-Origin: https://example.com

相关问题

has been blocked by CORS policy: No Access-Control-Allow-Origin header is present on the requested resource.

这个错误信息说明在发送请求时，服务器返回的响应头中没有包含Access-Control-Allow-Origin字段，导致浏览器拒绝接受该响应。这是由于跨域访问(Cross-Origin Resource Sharing，CORS)的限制所引起的。

为了解决这个问题，可以添加一个名为CorsConfig的配置类，其中配置了允许跨域访问的规则。具体做法是使用addCorsMappings方法将允许跨域访问的规则添加到CorsRegistry中，可以设置allowedOriginPatterns为"*"，表示允许来自所有域的请求；allowedHeaders设置为CorsConfiguration.ALL，表示允许所有请求头；allowedMethods设置为CorsConfiguration.ALL，表示允许所有请求方法；allowCredentials设置为true，表示允许发送身份验证信息；maxAge设置为3600，表示设置响应缓存的最大时间。通过这个配置类，服务器会在响应头中添加Access-Control-Allow-Origin字段，从而允许跨域访问。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
- *1* [has been blocked by CORS policy: No ‘Access-Control-Allow-Origin‘ header is present on the ...](https://blog.csdn.net/qq_45800640/article/details/118422632)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
- *2* [corsyusha:简单快速的代理，可在针对现有API进行原型设计时绕过CORS问题，而不必担心CORS](https://download.csdn.net/download/weixin_42176612/18261495)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
- *3* [解决前后端跨域报错：has been blocked by CORS policy: No ‘Access-Control-Allow-Origin](https://blog.csdn.net/wsaicyj/article/details/127814374)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v93^chatsearchT3_2"}}] [.reference_item style="max-width: 33.333333333333336%"]
[ .reference_list ]

has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

This error message usually occurs when a website or application is requesting resources from a different domain or server than the one it originated from. The browser enforces a security policy known as the "Same Origin Policy" to prevent malicious scripts from accessing resources from other domains without permission.

To fix this error, the server hosting the requested resource needs to include the "Access-Control-Allow-Origin" header in its response. This header specifies which domains are allowed to access the resource. If the header is not present or does not include the domain of the requesting website or application, the browser will block the request.

Web developers can also use techniques such as JSONP or CORS proxies to work around this error and access resources from other domains. However, these methods may introduce security risks and should be used with caution.