There are two easy methods as below,
1) Email validation. The most ordinary and well-known option to confirm the domain ownership. During the certificate activation, you will need to select the email address to which an approval email will be sent. Due to regulations of Certificate Authorities, it is only possible to use either a domain whois record or one of the following domain-related generic emails to receive an approver email: admin@example.com, administrator@example.com, postmaster@example.com, webmaster@example.com or hostmaster@example.com . After the enrollment process is completed, you will receive an email from the Certificate Authority to the selected email address.
To confirm the domain ownership rights for a COMODO certificate, you need to copy the validation code from the approval email, follow the link in it and paste the validation code into the corresponding field.
2) HTTP-based validation. It involves uploading of the activation file to the following directory of your site: <document_root>/.well-known/pki-validation/.
The text file can be retrieved after the enrollment process is completed. Right after the order submission, you will be brought to the certificate management page.
Once the file is uploaded and accessible externally via the following URL http://your_domain_name.com/.well-known/pki-validation/filename.txt
OR place "Auth File" at root directory of your website
If your CSR code contains www.domain.com as FQDN, please make sure that the file is available via the link http://domain.com/.well-known/pki-validation/file.txt OR http://domain.com/file.txt.
Content of the file shouldn't be changed in any way, as Comodo validation system is case sensitive.
