2.5.1.2.1 Simple Attribute Name Form
An attribute name in simple form is limited to referencing an attribute in the LocalClaims[] array (section 2.5.2) of the same name in simple form. An attribute name in simple form is case-insensitive and MAY contain any ALPHA or DIGIT (as specified in [RFC5234]) characters as well as the following characters: ":", ".", ", "_". An attribute name in simple form MAY also contain the "@" character in any position other than the first character of the attribute name. See attr-char1 in section 2.5.1.1 for encoding requirements.