subjectAltName field into the CSR, you must modify the [v3_req] section of your openssl.cnf file. By adding the directive copy_extensions = copyall, OpenSSL will automatically transfer all extensions defined in the configuration, including the email Subject Alternative Name, ensuring they appear correctly in the generated certificate request without manual intervention during the signing process.
Understanding the Configuration File Structure
The OpenSSL configuration file, typically located at /etc/ssl/openssl.cnf or a custom path specified via the -config flag, is divided into several sections. The most critical section for this task is [req], which defines how the Certificate Signing Request (CSR) is generated. Within this section, developers often define default distinguished names and extension handling rules. If you are managing multiple domains or services, it is helpful to review how other configurations interact with your mail server setup, such as Change Postfix Sender Envelope MAIL FROM Address To Match Return Path Header Email For Multiple Domains, to ensure consistency across your infrastructure.
By default, OpenSSL does not copy extensions from the configuration file into the CSR unless explicitly told to do so. This security feature prevents accidental inclusion of sensitive or invalid extensions. However, for internal certificates or specific organizational policies, copying these attributes is necessary to maintain accurate identity information.
Modifying the V3_REQ Section
To achieve the desired behavior, you need to locate or create the [v3_req] section in your openssl.cnf. This section is referenced by the req_extensions parameter within the [req] block. If this section does not exist, you should add it. Inside [v3_req], add the following line:
copy_extensions = copyallThis directive instructs OpenSSL to copy all extensions found in the configuration into the CSR. Alternatively, if you only want to copy the Subject Alternative Name (SAN) and ignore other potential extensions, you can use copy_extensions = copyonmatch. This ensures that only extensions present in both the configuration and the request context are transferred, reducing the risk of unintended data leakage.
After modifying the configuration file, verify that the [req] section points to this new section using req_extensions = v3_req. Without this linkage, OpenSSL will ignore the [v3_req] settings entirely, and your SAN entries will not be included in the final CSR.
Defining the Subject Alternative Name
Once the copying mechanism is enabled, you must define the actual email address in the [v3_req] section. Add the subjectAltName directive followed by the email address you wish to include. The syntax should look like this:
subjectAltName = email:[email protected]You can include multiple email addresses by separating them with commas. For example:
subjectAltName = email:[email protected], email:[email protected]It is crucial to ensure that the email addresses listed here match the intended recipients or administrators of the SSL certificate. Mismatches can lead to validation errors when browsers or clients attempt to verify the certificate's authenticity against the domain owner's identity.
Generating the CSR
With the configuration updated, generate the CSR using the standard OpenSSL command. Specify the configuration file using the -config option to ensure OpenSSL uses your modified settings rather than the system default.
openssl req -new -newkey rsa:2048 -nodes -keyout server.key -out server.csr -config /path/to/openssl.cnfDuring this process, OpenSSL will read the [v3_req] section, apply the copy_extensions directive, and embed the specified email addresses into the CSR. You can verify the contents of the generated CSR using the following command:
openssl req -in server.csr -text -nooutLook for the X509v3 Subject Alternative Name extension in the output. It should list the email addresses you defined in the configuration file. If they are missing, double-check the req_extensions setting in the [req] section and ensure there are no syntax errors in the openssl.cnf file.
Best Practices and Verification
Always test your configuration changes on a non-production environment first. Generating CSRs with incorrect SANs can lead to delays in certificate issuance or rejection by Certificate Authorities (CAs). Additionally, consider the implications of auto-deleting emails or other server-side automations that might interfere with certificate management workflows, similar to issues discussed in Automatically Deleted Postfix Emails.
Regularly audit your openssl.cnf files to ensure they remain secure and up-to-date. Outdated configurations may introduce vulnerabilities or fail to support newer cryptographic standards. By maintaining a clean and well-documented configuration file, you simplify the process of generating valid and compliant SSL certificates.
Frequently Asked Questions
What happens if I omit the config flag during CSR generation?
If you omit the -config flag, OpenSSL uses the system default configuration file, which likely lacks your custom copy_extensions setting. Consequently, the email SubjectAltName will not be copied into the CSR, resulting in an incomplete request that may be rejected by your CA.
Can I specify the email address directly on the command line instead of in the config file?
No, OpenSSL does not support specifying SubjectAltName extensions directly via command-line arguments for CSRs. You must define them in the configuration file under the [v3_req] section and enable copying via copy_extensions.
Does this method work for self-signed certificates as well?
Yes, but you must also configure the [v3_ca] section in your openssl.cnf file. When creating a self-signed certificate using openssl x509, the extensions are taken from the v3_ca section, not v3_req. Ensure both sections have consistent SAN definitions if you plan to sign the CSR locally.
How do I remove an existing email address from the SAN after configuration?
Edit the openssl.cnf file and remove the specific email entry from the subjectAltName line in the [v3_req] section. Then regenerate the CSR. Existing CSRs cannot be modified; you must create a new key pair or reuse the private key to generate a fresh CSR with the updated configuration.
Is it safe to use copyall for all extensions?
Using copyall is generally safe for internal CSRs where you control the configuration. However, for public-facing certificates submitted to third-party CAs, it is safer to use copyonmatch or explicitly list only the required extensions. This prevents accidental inclusion of unauthorized extensions that could cause validation failures.