Is it required to have 2-step authentication enabled on WordPress.com to use SSO?
jetpack_sso_require_two_step
jetpack_sso_require_two_step-
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filter jetpack_sso_match_by_emailLink the local account to an account on WordPress.com using the same email address.
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filter jetpack_sso_display_disclaimerFilter the display of the disclaimer message appearing when default WordPress login form is disabled.
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filter jetpack_sso_bypass_login_forward_wpcomRedirect the site’s log in form to WordPress.com’s log in form.
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filter jetpack_remove_login_formRemove the default log in form, only leave the WordPress.com log in button.
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action jetpack_sso_pre_handle_loginFires before Jetpack’s SSO modifies the log in form.
Jetpack Developer Resources 