You’d need to develop a plugin that supports their sso. It’s documented at Single Sign-On into WHMCS - WHMCS and DiscourseConnect - Official Single-Sign-On for Discourse (sso) other plugins that provide SSO support for other services. If you don’t have an engineering staff, you can post in marketplace. A wild guess for a budget is $2000-4000, but it might be easier or harder than I imagine.
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