E.g. add the following to only allow Persona logins from email.com and gmail.com email addresses.
persona_allowed_domains email.com,gmail.com
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# If persona_allowed_domains is set, check if the email address returned is on these domains.
# When not configured, allow all domains.
my $allowed_domains = $c->config->{persona_allowed_domains} || "";
if ( $allowed_domains ne "") {
my $email_ok = 0;
my @domains = split ',', $allowed_domains;
map { $_ =~ s/^\s*(.*?)\s*$/$1/ } @domains;