How to Generate and Digitally Sign a SAML Assertion within a SOAP Message using C#?

This C# code demonstrates generating a SAML assertion, digitally signing it, and embedding it within a SOAP message. Let's examine the code's functionality step-by-step:

SOAP Message Creation (CreateSoap Method):

The CreateSoap method constructs the basic SOAP message framework. This includes building the SOAP envelope, header, and body. Crucial elements like the To and Action addresses, MessageID, and the wsse:Security header are added. The wsse:Security header acts as a placeholder for the later-added, signed SAML assertion.

SAML Assertion Signing (SignXmlWithCertificate Method):

The SignXmlWithCertificate method handles the digital signature process for the SAML assertion. It takes the assertion element and an X509Certificate2 object as input. The signing process involves:

1. Creating a SignedXml object, initialized with the assertion element.
2. Setting the SigningKey property of SignedXml to the certificate's private key.
3. Creating a Reference object and adding it to SignedXml. The reference points to the data to be signed (an empty string here, signifying the entire assertion).
4. Creating a KeyInfo object and adding a KeyInfoX509Data clause containing the certificate.
5. Computing the signature using ComputeSignature and obtaining its XML representation via GetXml.
6. Appending the XML signature to the assertion element.

Subject Element Creation (CreateSubject Method):

The CreateSubject method adds the <subject></subject> element to the SAML assertion. This element contains subject-related information, such as name and confirmation method. In this example, the subject details are hardcoded.

Integration: Signed Assertion and SOAP Request:

Following the signing and subject creation, the signed assertion is integrated into the wsse:Security header. The SOAP body, currently holding placeholder data, can be replaced with the actual SOAP payload.

Saving the Signed XML:

Finally, the complete, digitally signed XML document is saved to a file.

How to Use:

To utilize this code:

1. Replace the certificate path (pfxpath) with the path to your certificate.
2. Ensure the SOAP body (xmlBytes) contains the correct XML request.
3. Execute the program.

The resulting XML file will contain the digitally signed SAML assertion embedded within the SOAP message. This output can be used for authentication or authorization with a remote system.

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