Symptoms
To enhance security, the Content Security Policy (CSP) restriction is added to all classic pages. If you have a customized classic page that contains customized domain content, the page may be blocked by the CSP restriction.
Resolution
Note: Make sure that the content of your customized domain is safe before you follow the instructions to unblock it.
To fix this issue, farm administrators can run the following commands to add the customized domain to the AllowIframeAppAuthorizePageDomains list:
add-pssnapin *
$f=get-spfarm
$f.AddGenericAllowedListValue("AllowIframeAppAuthorizePageDomains","<customized domain>")
$f.update()
After you run the commands, the customized domain will be included in the CSP's allowed domain list.
