How to dynamically generate -extfile parameter for openssl in bash script

I have a script that I use to generate development certificates for my .test domain. I managed to create PowerShell script to do this but I struggle to do the same in arch bash, usually -extfile expects a document is there a way I can generate a mock of file with bash function and pass it into it? Here is my script

#!/bin/bash

function gen_extfile()
{
	domain=$1
	cat << EOF 
		authorityKeyIdentifier=keyid,issuer\n
    basicConstraints=CA:FALSE\n
		keyUsage=digitalSignature,nonRepudiation,keyEncipherment,dataEncipherment\n
    subjectAltName = @alt_names\n
    [alt_names]\n
		DNS.1 = $domain
EOF
}


case "$1" in
    r*)
        [ -z "$2" ] && filename="rootCA" || filename="$2"
        openssl genrsa -des3 -passout pass:default -out "$filename.key" 4096
        openssl req -x509 -new -nodes -passin pass:default -key "$filename.key" -sha256 -days 20480 -subj "/C=GB/ST=London/L=London/O=Development/OU=IT Department/CN=Self Signed Certificate/emailAddress=info@example.com" -out rootCA.crt
    ;;
		h*)
        host="$2"
        destination="$3"
				if [ -z $host ]; then
            echo "Host argument is required"
            exit 1
        fi
				extFile=$(gen_extfile $host)
				openssl req -new -sha256 -nodes  -out "$host.csr" -newkey rsa:2048 -days 20480 -subj "/C=GB/ST=London/L=London/O=$host/OU=IT Department/CN=$host Self Signed Certificate/emailAddress=info@$host"  -keyout "$host.key"
				openssl x509 -req -passin pass:default -in "$host.csr" -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out "$host.crt" -days 500 -sha256 -extfile "$extFile"
        # openssl pkcs12 -export -passin pass:default  -inkey "$host.key" -in "$host.crt" -out "$host.pfx" -passout pass:
        # if ! [ -z $destination ]; then
        #     mv "$host*" $destination
        # fi
    ;;
    *) cat << EOF
ssl-cert: Generates 

Allowed options:
    root {?filename} {?destination} generates root certificate. Default cirtificate basename is rootCA 
    host {host} {?destination}      generates domain certificate
EOF
esac

Here is the solution that worked for me.

#!/bin/bash

function gen_extfile()
{
	domain=$1
	cat << EOF 
		authorityKeyIdentifier=keyid,issuer\n
    basicConstraints=CA:FALSE\n
		keyUsage=digitalSignature,nonRepudiation,keyEncipherment,dataEncipherment\n
    subjectAltName = @alt_names\n
    [alt_names]\n
		DNS.1 = $domain
EOF
}


case "$1" in
    r*)
        [ -z "$2" ] && filename="rootCA" || filename="$2"
        openssl genrsa -des3 -passout pass:default -out "$filename.key" 4096
        openssl req -x509 -new -nodes -passin pass:default -key "$filename.key" -sha256 -days 20480 -subj "/C=GB/ST=London/L=London/O=Development/OU=IT Department/CN=Self Signed Certificate/emailAddress=info@example.com" -out rootCA.crt
    ;;
		h*)
        host="$2"
        destination="$3"
				if [ -z $host ]; then
            echo "Host argument is required"
            exit 1
        fi
				extFile=$(gen_extfile $host)
				openssl req -new -sha256 -nodes  -out "$host.csr" -newkey rsa:2048 -days 20480 -subj "/C=GB/ST=London/L=London/O=$host/OU=IT Department/CN=$host Self Signed Certificate/emailAddress=info@$host"  -keyout "$host.key"
				openssl x509 -req -passin pass:default -in "$host.csr" -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out "$host.crt" -days 500 -sha256 -extfile <(printf "$extFile")
        openssl pkcs12 -export -passin pass:default  -inkey "$host.key" -in "$host.crt" -out "$host.pfx" -passout pass:
        if ! [ -z $destination ]; then
            mv "$host*" $destination
        fi
    ;;
    *) cat << EOF
ssl-cert: Generates 

Allowed options:
    root {?filename} {?destination} generates root certificate. Default cirtificate basename is rootCA 
    host {host} {?destination}      generates domain certificate
EOF
esac