Use Dev Proxy with .NET applications running in Docker

If you run your .NET application in a Docker container and want to use Dev Proxy, there are several steps you need to follow to make it work.

Configure proxy for your Docker container

Because your .NET app is running inside a Docker container and Dev Proxy is running on your host, you need to configure the proxy to point to the IP address of your computer (http://192.0.2.13 in the following example). .NET uses the HTTPS_PROXY environment variable to configure the proxy for its HTTP client. To configure the variable for your Docker container, use the --env, -e option when starting the container:

docker run --rm -it -v $(pwd):/usr/src/app -e HTTPS_PROXY=http://192.0.2.13:8000 mcr.microsoft.com/dotnet/sdk:8.0 bash

devproxy --ip-address 0.0.0.0

devproxy --ip-address 0.0.0.0

Handle SSL certificates

Dev Proxy uses its own SSL certificate to inspect HTTPS traffic intercepted from your application. When you install Dev Proxy on your computer, it generates a self-signed SSL certificate and adds it to the list of trusted certificates. However, when running your application in a Docker container, the container doesn't have access to the SSL certificate installed on your computer. There are two ways for you to handle SSL certificates when using Dev Proxy with .NET applications running in Docker containers.

Configure Dev Proxy certificate in your Docker container

To allow Dev Proxy to inspect HTTPS requests, you can configure the Dev Proxy SSL certificate as trusted in your Docker container.

Start, by exporting the Dev Proxy certificate to PEM.

$proxyPath = "C:\apps\devproxy"
$gitPath = "C:\Program Files\Git"

# convert Dev Proxy root certificate to PEM
$executable = "${gitPath}\usr\bin\openssl.exe"
$arguments = 'pkcs12 -in "{0}\rootCert.pfx" -out "{0}\rootCert.crt" -nodes' -f $proxyPath
Start-Process -FilePath $executable -ArgumentList $arguments -NoNewWindow -Wait

# Read PEM contents
$content = Get-Content "$proxyPath\rootCert.crt"

# Find the indices of the begin and end certificate lines
$beginIndex = $content.IndexOf("-----BEGIN CERTIFICATE-----")
$endIndex = $content.IndexOf("-----END CERTIFICATE-----")

# If both lines are found
if ($beginIndex -ne -1 -and $endIndex -ne -1) {
    # Trim the content to only include the certificate
    $content = $content[$beginIndex..$endIndex]
}

# Write the updated content back to the file
$content | Out-File "$proxyPath\dev-proxy-ca.crt"

# export Dev Proxy certificate
security find-certificate -c "Dev Proxy CA" -a -p > dev-proxy-ca.pem
# rename to .crt
mv dev-proxy-ca.pem dev-proxy-ca.crt

# export Dev Proxy certificate
openssl pkcs12 -in ~/.config/dev-proxy/rootCert.pfx -clcerts -nokeys -out dev-proxy-ca.crt -passin pass:""
# rename to .crt
mv dev-proxy-ca.pem dev-proxy-ca.crt

Next, copy the certificate to your Docker container. The easiest way to copy the certificate is to copy it to the project folder, which you mount to the container.

Then, in the Docker container, trust the certificate. If you're using the mcr.microsoft.com/dotnet/sdk image, you can use the following commands:

# change to the directory where your application is located
cd /usr/app/src
# copy the certificate to the trusted certificates directory
cp dev-proxy-ca.crt /usr/local/share/ca-certificates
# update the trusted certificates
update-ca-certificates

Ignore SSL certificate validation in your .NET application

Another way to handle SSL certificates when using Dev Proxy with .NET applications running in Docker containers is to ignore SSL certificate validation in your application. This approach requires you to modify your application code.

In your application, add the following code to ignore SSL certificate validation:

ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true;