istio.io/content/help/faq/mixer/header-rules.md

title	weight
Why does my rule not match?	50

Mixer rules must be valid to be applied at runtime. That means the match conditions are well-defined expressions in the language, the attributes are declared in an attribute manifest, and rules have no dangling references to handlers and instances.

The attribute values are typically normalized before evaluating rules on them. For example, HTTP headers have lowercase keys in request.headers and response.headers attributes. An expression request.headers["X-Forwarded-Proto"] == "http" does not match any request even though HTTP headers are case-insensitive. Instead, use an expression request.headers["x-forwarded-proto"] == "http".