Attaching client certificates

Introduction

Fiddler2 includes the ability to decrypt, view, and modify HTTPS-secured traffic for debugging purposes.  This feature is disabled by default, but can be enabled in Fiddler's Tools > Fiddler Options dialog.

See Decrypting HTTPS traffic with Fiddler2 for more information on HTTPS decryption support in Fiddler.

Fiddler's HTTPS decryption feature also offers basic support for intercepting requests that require client certificates and responding with a client certificate from the machine running Fiddler.

Selection of Client Certificate

If a .CER file has been specified for a given session as follows:

oSession["https-Client-Certificate"] = "C:\\test\\someCert.cer";

Then, Fiddler will simply use that certificate for the current session.

Otherwise, Fiddler does not have the capability to prompt for a client certificate itself. 

• Fiddler will always use the first acceptable certificate (per the server's Acceptable issuers list) in the Windows certificate store on the machine running Fiddler. 

• If no acceptable certificates are found in the Windows store, Fiddler will look for the file %USERPROFILE%\My Documents\Fiddler2\ClientCertificate.cer and attach that certificate.

Using the certificate from a SmartCard

If you export a .CER from the SmartCard certificate, Fiddler will use the matching certificate from the smartcard to authenticate to the server.

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