Client Certificates Request Entity Too Large

After switching on Client Certificates for a WCF service I've been working on, I decided to go and test a bunch of different messages. I've been using the same few "developer" test messages, you know, the ones that work every time.

Well, upon sending one of the larger messages, I suddenly received the following error:

HTTP Error 413.0 - Request Entity Too Large

The page was not displayed because the request entity is too large.

It then gave some helpful hints (not being sarcastic here)

Most Likely Causes

The Web server is refusing to service the request because the request entity is too large.
The Web server cannot service the request because it is trying to negotiate a client certificate but the request entity is too large.
The request URL or the physical mapping to the URL (i.e., the physical file system path to the URL's content) is too long.

Things you can try:

Verify that the request is valid.
If using client certificates, try:
Increasing system.webServer/serverRuntime@uploadReadAheadSize
Configure your SSL endpoint to negotiate client certificates as part of the initial SSL handshake. (netsh http add sslcert ... clientcertnegotiation=enable)

I decided to try the the first suggestion. I went to C:\Windows\System32\inetsrv and opened up the applicationHost.config file. Like the error suggests, I looked into how to add this updated value. I found a section already defined for the service I was trying to target:

<location path="Default Web Site/MyService">
    <system.webServer>
        <security>
            <access sslFlags="Ssl, SslNegotiateCert, SslRequireCert" />
        </security>
    </system.webServer>
</location>

So, I then added the element <serverRuntime uploadReadAheadSize="2147483647" /> and altogether it looks like this:

<location path="Default Web Site/MyService">
    <system.webServer>
        <security>
            <access sslFlags="Ssl, SslNegotiateCert, SslRequireCert" />
        </security>
        <serverRuntime uploadReadAheadSize="2147483647" />
    </system.webServer>
</location>

I went and restarted IIS, tried the large message again and still received the error. After firing up Google to search for more help, I ended finding a post in a thread on the IIS forums which mentions using the appcmd.exe program to enter the setting:

appcmd.exe set config -section:system.webserver/serverruntime /uploadreadaheadsize:2147483647 /commit:apphost

After issuing the command, everything worked. If you want to issue the command at a site-level vs. machine-level, try the following:

appcmd.exe set config "Default Web Site/MyService" /section:system.webserver/serverruntime /uploadreadaheadsize:2147483647 /commit:APPHOST

That should get everything up and running...it did for me.

Any comments or suggestions, please let me know via Twitter.

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HTTP Error 413.0 - Request Entity Too Large