docs: Add documentation for generating certificate signing request

Signed-off-by: Krzysztof Piotrowski <[email protected]>

docs/src/operate/security/certificate-signing-request.md

@@ -0,0 +1,78 @@
+---
+title: Certificate signing request
+tags: [Operate, Security, Cloud]
+description: Generate certificate signing request for %%te%%
+---
+
+If you want to use a device certificate which is signed by a Certificate Authority (CA), you can generate the Certificate Signing Request (CSR), which is later used by CA to generate a device certificate. This process requires additional tooling as %%te%% provides you only with the CSR. 
+
+## Create a certificate signing request
+
+To create a CSR you can use [`tedge cert create-csr`](../../references/cli/tedge-cert.md) %%te%% command:
+
+```sh
+sudo tedge cert create-csr --device-id alpha
+```
+
+or
+
+```sh
+sudo tedge cert create-csr
+```
+if public key already exists and you want to reuse device name.
+
+```text title="Output"
+Certificate Signing Request was successfully created.
+```
+
+:::note
+`tedge cert` requires `sudo` privilege. This command provides no output on success.
+:::
+
+[`sudo tedge cert create-csr`](../../references/cli/tedge-cert.md) creates the certificate signing request in a default location (`/etc/tedge/device-certs/`).
+To use a custom location, refer to [`tedge config`](../../references/cli/tedge-config.md).
+
+Now you should have a CSR in the `/etc/tedge/device-certs/` directory.
+
+```sh
+ls -l /etc/tedge/device-certs/
+```
+
+```text title="Output"
+total 8
+-r--r--r-- 1 mosquitto mosquitto 664 May 31 09:26 tedge-csr.csr
+-r-------- 1 mosquitto mosquitto 246 May 31 09:26 tedge-private-key.pem
+```
+
+:::note
+`tedge cert create-csr` will reuse private key if it was already created, e.g by the `tedge cert create` command
+:::
+
+## Errors
+
+### Certificate Signing Request creation fails due to invalid device id
+
+If non-supported characters are used for the device id then the cert create-csr will fail with below error:
+
+```text
+Error: failed to Generate the Certificate Signing Request.
+
+Caused by:
+    0: DeviceID Error
+    1: The string '"+"' contains characters which cannot be used in a name [use only A-Z, a-z, 0-9, ' = ( ) , - . ? % * _ ! @]
+```
+
+
+### Certificate Signing Request already exists in the given location
+
+If the CSR file already exists you may see following error:
+
+```text
+Error: failed to Generate the Certificate Signing Request.
+
+Caused by:
+    A certificate already exists and would be overwritten.
+            Existing file: "/etc/tedge/device-certs/tedge-csr.csr"
+```
+
+Remove the CSR file manually and try executing [`tedge cert create-csr`](../../references/cli/tedge-cert.md) again.

docs/src/references/cli/tedge-cert.md

@@ -38,6 +38,20 @@ OPTIONS:
     -h, --help              Print help information
 ```
 
+## Create-csr
+
+```sh title="tedge cert create-csr"
+tedge-cert-create-csr 
+Create certificate signing request
+
+Usage: tedge cert create-csr [OPTIONS]
+
+Options:
+      --device-id <ID>           The device identifier to be used as the common name for the certificate
+      --config-dir <CONFIG_DIR>  [default: /etc/tedge]
+  -h, --help                     Print help
+```
+
 ## Show
 
 ```sh title="tedge cert show"