How to configure multiple subdomain with SSL in Apache?
Change your virtualhost code for wildcard (*.example.com) for all sub-domain, to implement this feature your SSL certificate should be a wildcard which supports for multiple sub-domains
Change / add two lines in <virtualhost> code of apache httpd.conf or ssl.conf file
ServerName www.example.com ServerAlias *.example.comExamples :
a.example.comb.example.comWHATEVER_SUB-DOMAIN_TEXT.example.com