Custom SSO confirm page

Reference: https://element-hq.github.io/synapse/latest/templates.html#html-page-templates-for-single-sign-on-sso

redirect_url: {{redirect_url}}

description: {{description}}
idp_id: {{idp.idp_id}}
idp_name: {{idp.idp_name}}
idp_icon: {{idp.idp_icon}}
idp_brand: {{idp.idp_brand}}