Gets the signature algorithm OID string from the certificate.
An OID is represented by a set of nonnegative whole numbers separated
by periods.
For example, the string "1.2.840.10040.4.3" identifies the SHA-1
with DSA signature algorithm defined in
<a href="http://www.ietf.org/rfc/rfc3279.txt">RFC 3279: Algorithms and
Identifiers for the Internet X.509 Public Key Infrastructure Certificate
and CRL Profile</a>.
<p>See {@link #getSigAlgName() getSigAlgName} for
relevant ASN.1 definitions.
Gets the signature algorithm OID string from the certificate. An OID is represented by a set of nonnegative whole numbers separated by periods. For example, the string "1.2.840.10040.4.3" identifies the SHA-1 with DSA signature algorithm defined in <a href="http://www.ietf.org/rfc/rfc3279.txt">RFC 3279: Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and CRL Profile</a>.
<p>See {@link #getSigAlgName() getSigAlgName} for relevant ASN.1 definitions.
@return the signature algorithm OID string.