encodeHeader filter

[szuecs]

Is your feature request related to a problem? Please describe.

A discussion in slack showed that there is a missing feature to change a string value encoding of headers if backend assumes a certain encoding.

Describe the solution you would like

I expect that this would solve the problem generic enough. It would read the value in header "X-Foo" decode by utf-8 and encode it with iso-8859-1 and replace the value of "X-Foo" header:

encodeHeader("X-Foo", "utf-8", "iso-8859-1")

Additional context (optional)

https://www.rfc-editor.org/rfc/rfc7230#section-3.2.4

Historically, HTTP has allowed field content with text in the
ISO-8859-1 charset [ISO-8859-1], supporting other charsets only
through use of [RFC2047] encoding. In practice, most HTTP header
field values use only a subset of the US-ASCII charset [USASCII].
Newly defined header fields SHOULD limit their field values to
US-ASCII octets. A recipient SHOULD treat other octets in field
content (obs-text) as opaque data.