Java Security

Hello,

We are implementing SSO with a client and they don't work with certificates but with the RSA key itself.
Below is an example of the file they expect to exchange which is the RSA public key:

<RSAKeyValue><Modulus>0siL9/q6RKwrrwEu0g1uP4bqNv+9moUdxDOG2CqgPWUbBrvT9Wbzp9ujQHJ73Wu+hgNWMKmm7gxUZfaK52Yq9dsjTS8RMBUT78SGjJe77mmE0jryaw3Dtvk3Ax8bOlStJUXPsE2uuDrb5PblrOVR6zb3GVGryT8zhD+sYk67RI0=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>

I am trying to develop a utility that will convert this into a standard X509 certificate file and was able to find a very useful code in the Bouncy Castle API.
The API expects the object PublicKey so what I need is to create an RSAPublicKey object from the information above.
The RSAPublicKeySpec can help but it expects the Modulus and the Exponent as BigIntegers.
Any idea how can I convert the Modulus and the Exponent above to valid BigIntegers without compromising the data?

Thanks,
Roy