Constant CONTENT_SECURITY_POLICY 

pub const CONTENT_SECURITY_POLICY: &str = "default-src 'self'; img-src 'self' data:; \
     style-src 'self'; script-src 'self'; object-src 'none'; frame-ancestors 'none'; \
     base-uri 'self'; form-action 'self'";

Content-Security-Policy of every response that does not set its own (the desktop sign-in page derives its policy from it).