question: public static byte [ ] convertDEREncodedSignatureToJWSConcatenated ( final byte [ ] derEncodedSignatureValue ) throws IOException { final ASN1InputStream asn1InputStream = new ASN1InputStream ( derEncodedSignatureValue ) ; final ASN1Primitive asn1Primitive = asn1InputStream . readObject ( ) ; asn1InputStream . close ( ) ; final ASN1Sequence asn1Sequence = ( ASN1Sequence . getInstance ( asn1Primitive ) ) ; final ASN1Integer rASN1 = ( ASN1Integer ) asn1Sequence . getObjectAt ( 0 ) ; final ASN1Integer sASN1 = ( ASN1Integer ) asn1Sequence . getObjectAt ( 1 ) ; final X9IntegerConverter x9IntegerConverter = new X9IntegerConverter ( ) ; final byte [ ] r = x9IntegerConverter . integerToBytes ( rASN1 . getValue ( ) , 32 ) ; final byte [ ] s = x9IntegerConverter . integerToBytes ( sASN1 . getValue ( ) , 32 ) ; final byte [ ] concatenatedSignatureValue = new byte [ 64 ] ; System . arraycopy ( r , 0 , concatenatedSignatureValue , 0 , 32 ) ; System . arraycopy ( s , 0 , concatenatedSignatureValue , 32 , 32 ) ; return concatenatedSignatureValue ; }
target:  Helper method to convert DER-encoded signature values (e.g. used by Java) to concatenated signature values (as used by the JWS-standard)