Update basic auth filter to consume base64 encoded password

[bianpengyuan]

Currently basic auth filter only consumes plain text username:passwd. This is to track the work to make it read base64 encoded username:passwd instead.

[mboveri]

Would this also add functionality to allow the basic auth filter to be able to consume from a Kubernetes secret or environment variable generated by a Kubernetes secret?

[bianpengyuan]

Yeah it depends on this: proxy-wasm/proxy-wasm-cpp-host#127

[bianpengyuan]

And envoy just added support for Wasm env variable read: envoyproxy/envoy#14958 I can add some support based on that.

[mboveri]

That would be great!

[johnzheng1975]

And envoy just added support for Wasm env variable read: envoyproxy/envoy#14958 I can add some support based on that.

@bianpengyuan , had istio supported this -- wasm can read env variable from istio-proxy now? Can you provide some example. Thanks.