Rust TLS Reqwest Error The Certificate Was Not Trusted Troubleshooting And Solutions

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Hey guys! Ever run into the frustrating "The certificate was not trusted" error when trying to make HTTPS requests with Rust's reqwest library? It's a common head-scratcher, especially when you're working with local development environments and self-signed certificates. Let's dive into why this happens and, more importantly, how to fix it!

Understanding the "The certificate was not trusted" Error

When you encounter this TLS error, it basically means that your Rust application, using reqwest, doesn't trust the SSL/TLS certificate presented by the server it's trying to connect to. This usually happens in a few key scenarios:

  • Self-Signed Certificates: This is super common in local development. When you set up SSL for your local Rails backend (or any other local server), you often generate a self-signed certificate. These certificates aren't issued by a trusted Certificate Authority (CA) like Let's Encrypt or DigiCert, so your system doesn't automatically trust them.
  • Missing Intermediate Certificates: Sometimes, a server's certificate chain isn't complete. This means that while the server's certificate itself might be valid, the intermediate certificates needed to establish the chain of trust back to a root CA are missing.
  • Certificate Mismatch: The hostname in the URL you're trying to access doesn't match the hostname(s) listed in the certificate. This is a security measure to prevent man-in-the-middle attacks.
  • Expired or Revoked Certificates: Although less common in local development, if the certificate has expired or been revoked, you'll also see this error.

In the context of your situation, where you're running a Rails backend locally with SSL and Puma, the most likely culprit is a self-signed certificate. Your Rust application, using reqwest, is saying, "Hey, I don't recognize this certificate authority, so I'm not trusting this connection!"

Solutions to Fix the Rust TLS Reqwest Certificate Error

Okay, so how do we get around this? Here are a few approaches, ranging from the quick-and-dirty to the more robust:

1. The Insecure (But Quick) Fix: Disabling Certificate Verification

Disclaimer: I'm putting this first, but I also want to emphasize that this is generally not recommended for production environments. Disabling certificate verification defeats the purpose of TLS, which is to ensure secure communication. However, for local development, it can be a quick way to get things working.

In reqwest, you can disable certificate verification using the danger_accept_invalid_certs method:

use reqwest::Client;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::builder()
        .danger_accept_invalid_certs(true)
        .build()?;

    let response = client.get("https://your-local-rails-app.test:3000") // Replace with your URL
        .send()
        .await?;

    println!("Status: {}", response.status());
    Ok(())
}

What's happening here? We're telling reqwest to ignore certificate validation errors. This means it will accept any certificate, even if it's self-signed, expired, or doesn't match the hostname. Again, use this cautiously and only in development.

2. Adding Your Self-Signed Certificate to the Trusted Store

This is the more secure and recommended approach for local development. You're essentially telling your system (and thus, reqwest) to trust your self-signed certificate.

Here's the general process:

  1. Locate your certificate file: This is usually a .crt or .pem file that you generated when setting up SSL for your Rails backend. If you used openssl, it might be something like server.crt.

  2. Add the certificate to your system's trusted store. The exact steps for this vary depending on your operating system:

    • macOS:
      1. Open Keychain Access (search for it in Spotlight).
      2. Drag and drop your certificate file into the System keychain.
      3. Double-click the certificate.
      4. Expand the Trust section.
      5. In the "When using this certificate" dropdown, select "Always Trust".
      6. Close the certificate window. You might be prompted for your password.
    • Windows:
      1. Double-click the certificate file.
      2. The Certificate Import Wizard will open. Select "Local Machine" and click Next.
      3. Choose "Place all certificates in the following store" and click Browse.
      4. Select "Trusted Root Certification Authorities" and click OK, then Next.
      5. Click Finish.
    • Linux (Ubuntu/Debian):
      1. Copy your certificate file to /usr/local/share/ca-certificates/: sudo cp your_certificate.crt /usr/local/share/ca-certificates/
      2. Update the certificate store: sudo update-ca-certificates

  3. Restart your Rust application: After adding the certificate, you might need to restart your application for the changes to take effect.

Why does this work? By adding the certificate to your system's trusted store, you're telling your operating system (and any applications that rely on its trust store, like reqwest) that this certificate is safe to trust. This ensures that secure communication can proceed without errors. You're essentially creating a more reliable and trustworthy local development environment.

3. Explicitly Loading the Certificate in reqwest

Another approach is to tell reqwest specifically to trust your certificate by loading it directly in your code. This is useful if you want to keep your certificate handling within your application's configuration rather than relying on the system's trust store.

use reqwest::Client;
use std::fs;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let cert = fs::read("path/to/your/certificate.crt")?; // Replace with the actual path
    let provider = reqwest::Certificate::from_pem(&cert)?;

    let client = Client::builder()
        .add_root_certificate(provider)
        .build()?;

    let response = client.get("https://your-local-rails-app.test:3000") // Replace with your URL
        .send()
        .await?;

    println!("Status: {}", response.status());
    Ok(())
}

What's going on here?

  1. We read the contents of your certificate file using fs::read. This crucial step ensures that the certificate data is accessible to the application.
  2. We create a reqwest::Certificate from the PEM-encoded data using Certificate::from_pem. This converts the raw certificate data into a format that reqwest can understand.
  3. We add this certificate as a root certificate to the reqwest client builder using .add_root_certificate(provider). This action explicitly instructs reqwest to trust this certificate for the current connection.

This method is more explicit and keeps the certificate handling within your application's scope. It's particularly useful if you have a specific certificate you want to trust for a particular connection, without affecting the system-wide trust store. By managing certificates within the application, you gain finer-grained control over security settings.

4. Addressing Missing Intermediate Certificates

If the issue isn't a self-signed certificate, but rather missing intermediate certificates, you'll need to ensure your server is sending the full certificate chain. This usually involves configuring your web server (e.g., Puma in your case) to include the intermediate certificates in the SSL configuration.

How to check for missing intermediate certificates:

You can use online tools like SSL Labs' SSL Server Test (https://www.ssllabs.com/ssltest/) to analyze your server's SSL configuration. It will tell you if your certificate chain is complete.

How to fix it:

  1. Obtain the intermediate certificates: Your CA (the organization that issued your certificate) should provide these. They're often in a .pem or .crt file.
  2. Configure your web server: The exact steps depend on your web server. For Puma, you'd typically concatenate your server certificate and the intermediate certificates into a single file and configure Puma to use that file.

5. Certificate Mismatch Issues

If you're seeing a certificate mismatch error (the hostname in the URL doesn't match the certificate), double-check the following:

  • Your URL: Make sure you're using the correct hostname in your Rust code. If your certificate is for your-local-rails-app.test, you need to use that exact hostname in your reqwest calls.
  • Your certificate's Subject Alternative Names (SANs): A certificate can have multiple hostnames associated with it through SANs. Check your certificate's SANs to see if the hostname you're using is included.

If the hostname is incorrect, either update your URL or regenerate your certificate with the correct hostname.

Back to Your Specific Situation

Given that you're running a local Rails backend with SSL and Puma, starting with solution #2 (adding your self-signed certificate to the trusted store) is the most likely path to success. It's a good balance between security and convenience for local development.

If that doesn't work, double-check your certificate configuration in Puma and make sure you're using the correct hostname in your Rust application. Also, consider explicitly loading the certificate in reqwest as shown in solution #3.

Conclusion

Troubleshooting TLS errors can be a bit of a rabbit hole, but hopefully, this guide has given you a solid understanding of the "The certificate was not trusted" error in reqwest and how to fix it. Remember to prioritize security, especially in production, but don't be afraid to use the quick fixes for local development when appropriate. Good luck, and happy coding!

If you have any questions, feel free to ask!