When you export your SSL certificates to a pfx file, name the certificate the same thing that will be used as the host header value for your SSL binding. This designation is how the correct certificate is located and loaded for a site since you no longer bind a specific SSL certificate to a site when using this configuration.
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Wildcard certificate
The IIS provider uses the underscore character as a special character to indicate that it is a wildcard certificate. If the subject name in the SSL certificate is *.contoso.com, then the file name should be "_.contoso.com.pfx". NOTE: IIS provider would first try to search for a SSL certificate with the filename that exactly matches the domain name of the destination site. For example, if the destination site is www.contoso.com, the IIS provider first tries to locate www.consoto.com.pfx. If that is unsuccessful, then it tries to locate _.contoso.com
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