https://stackoverflow.com/questions/40871983/rewritecond-comparing-two-variables-in-apache-htaccess
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In RewriteCond you cannot use a variable on right hand side.

You have to use it like this:

RewriteCond %{HTTP_HOST}##%{HTTP:Origin} ^(.+)##http://\1(/|$)

Here are are joining 2 variables using a delimiter ## (it can be anything). Then on RHS we match and capture value before ## that represents HTTP_HOST. After ## using a back-reference \1 we do our matching.