this is what i've got in my init.vim and it works okay:

-- hack to get authzed working until it's packaged
local parser_config = require'nvim-treesitter.parsers'.get_parser_configs()

parser_config.authzed = {
        install_info = {
                url = "https://github.com/mleonidas/tree-sitter-authzed", -- local path or git repo
                files = { "src/parser.c" },
                generate_requires_npm = false,
                requires_generate_from_grammar = false,
                -- optional entries:
                branch = "main", -- default branch in case of git repo if different from master
        },
        filetype = "zed", -- if filetype does not match the parser name
}
EOF

" Get zed highlighting working by default
augroup Authzed
  au!
  autocmd BufNewFile,BufRead *.authzed set ft=zed
  autocmd BufNewFile,BufRead *.zed set ft=zed
  autocmd BufNewFile,BufRead *.azd set ft=zed
augroup END