What is an XML-based open standard for exchanging authentication and authorization information and is commonly used for web applications?

SAML.

Explanation:

SAML seems to be an accessible standardized XML-based for some of the sharing of validation and verification details and has been generally implemented for the web apps and it seems to be a design that would be SSO. Verification data is shared via XML documentation which are securely signed. So, the following answer is correct according to the given scenario.

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