Allow configuration of Signature Algorithm for SAML

To configure a signature algorithm for SAML, add a SignatureAlgorithm entry to the plugin <parameters> , for instance: <parameter name= "SignatureAlgorithm" > http://www.w3.org/2001/04/xmldsig-more#rsa-sha256 </parameter> The signature algorithms are defined by the various SAML and XML specs, in particular RFC 6931 . If an algorithm unknown to the current library has to be used, the following more verbose syntax that includes the explicit JCA/JCE key algorithm specifier ( RSA in this example) may be used: <parameter name= "SignatureAlgorithm.RSA" > http://www.w3.org/2001/04/xmldsig-more#rsa-sha256 </parameter> In the same way it's possible to define a digest algorithm with the DigestAlgorithm parameter: <parameter name= "DigestAlgorithm" > http://www.w3.org/2001/04/xmlenc#sha256 </parameter> Consult the normative documents like W3C XML Encryption for the algorithms.