Represents the "Prop_AuthType" entry of the signature dictionary object.

It is an optional entry defined as part of the PDF 1.5 specification.

It contains a string representing a PDF name object.

This item may take one of the following valid values:.

• PIN
• Password
• Fingerprint

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 252, page 469.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 255, page 567.