Azure AD supports B2B Direct Federation (preview) with third party identity providers that support either SAML 2.0 or WS-Fed. B2B guest users from the third-party identity provider can use their existing accounts to sign into your Azure AD tenant, and you can then grant them access to some of your applications.
AWS Cognito supports SAML 2.0, so you should be able to configure Direct Federation. For instructions on how to set up Direct Federation in Azure AD, see B2B Direct Federation.