.htaccess HTTPS redirect without changing url

Question

I have a main domain mydomain.com and a subdomain m.mydomain.com , both are SSL secured.

When I access the subdomain m.mydomain.com I want to be redirected on mydomain.com/mobile.php/nb without changing the url...so the url must remain m.mydomain.com

Here is what I came up:

RewriteEngine on  
RewriteCond %{HTTP_HOST} ^m\.mydomain\.com$ [OR]  
RewriteCond %{HTTP_HOST} ^www\.m\.mydomain\.com$  
RewriteCond %{REQUEST_URI} !^/\.well-known/cpanel-dcv/[0-9a-zA-Z_-]+$  
RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0-9]{32}\.txt(?:\ Comodo\ DCV)?$  
RewriteRule ^(.*)$ "https\:\/\/mydomain\.com\/mobile\.php\/nb$1" [R=301,L]  

It redirects me right but it doesn't keep the subdomain url address.

All the solutions I've found works only if the sites are not secured(http).

Answer 1

It can, but shouldn't be done via the .htaccess file.
This is normally done wihtin your vhost config file

<VirtualHost *:80>
    ServerName www.example.com
    Redirect / https://secure.example.com/
</VirtualHost>

<VirtualHost _default_:443>
    ServerName secure.example.com
    DocumentRoot /usr/local/apache2/htdocs
    SSLEngine On
    # etc...
</VirtualHost>

Source: https://wiki.apache.org/httpd/RedirectSSL

Answer 2

The mod-rewrite R flag performs an external redirection of urls from old location to the new one. If you do not want to redirect your subdomain remove the R=301 flag from your RewriteRule and use an absolute path instead of the full url as Rewrite destination.

RewriteEngine on

RewriteCond %{HTTP_HOST} ^(www\.)?m\.mydomain\.com$ [NC]
RewriteCond %{REQUEST_URI} !^/\.well-known/cpanel-dcv/[ 0- 9a -zA-Z_-]+$
RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0- 9]{ 32 }\.txt(?:\Comodo\DCV)?$
RewriteRule ^(.*)$ /mobile.php/nb/$1 [L]

This will internally redirect www.m.domain.com or m.domain.com to /mobile.php/nb/ .