can we share user login in 2 wordpress installs in 2 subdomains on one server? [duplicate]

See my answer on this exact problem. Long story short, you also need to define COOKIEHASH, otherwise the login cookie names will be different for each site:

define( 'COOKIEHASH', 'randomhash' );

Make sure to change randomhash to a real hash, you can grab one here.

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