Add docs about the TLS usage

README.md

@@ -72,6 +72,7 @@ The config file is automatically migrated when GitLab Runner was installed from
 
 ### Advanced Configuration
 
+* [See the self-signed certificates](docs/configuration/tls-self-signed.md)
 * [See advanced configuration options](docs/configuration/advanced-configuration.md)
 * [See example configuration file](config.toml.example)
 * [See security considerations](docs/security/index.md)

docs/configuration/advanced-configuration.md

@@ -28,6 +28,8 @@ This defines one runner entry.
 | `name`              | not used, just informatory |
 | `url`               | CI URL |
 | `token`             | runner token |
+| `tls-ca-file`       | file containing the certificates to verify the peer when using HTTPS |
+| `tls-skip-verify`   | whether to verify the TLS certificate when using HTTPS, default: false |
 | `limit`             | limit how many jobs can be handled concurrently by this token. 0 simply means don't limit |
 | `executor`          | select how a project should be built, see next section |
 | `shell`             | the name of shell to generate the script (default value is platform dependent) |

docs/configuration/tls-self-signed.md

+## The self-signed certificates or custom Certification Authorities
+
+Since version 0.7.0 the GitLab Runner have allows to configure certificates that are used to verify TLS peer when connecting GitLab server.
+
+**This allows to solve the `x509: certificate signed by unknown authority` problem when registering runner.**
+
+The GitLab Runner provides these options:
+
+1. **Default**: GitLab Runner reads system certificate store and verifies the GitLab server against the CA's stored in system.
+
+2. GitLab Runner reads the PEM (**DER format is not supported**) certificate from predefined file:
+
+    - `/etc/gitlab-runner/certs/hostname.crt` on *nix systems when gitlab-runner is executed as root.
+    - `~/.gitlab-runner/certs/hostname.crt` on *nix systems when gitlab-runner is executed as non-root,
+    - `./certs/hostname.crt` on other systems.
+        
+    If address of your server is: `https://my.gitlab.server.com:8443/`.
+    Create the certificate file at: `/etc/gitlab-runner/certs/my.gitlab.server.com`. 
+
+3. GitLab Runner exposes `tls-ca-file` option during registration and in [`config.toml`](advanced-configuration.md)
+which allows you to specify custom file with certificates. This file will be read everytime when runner tries to
+access the GitLab server.
+
+4. GitLab Runner exposes `tls-skip-verify` option during registration and [`config.toml`](advanced-configuration.md)
+which allows you to skip TLS verification when connecting to server.
+**This approach is INSECURE! Use at your own risk!**
+Anyone can eavesdrop your connection:
+- see the runner token which is used to authenticate against GitLab,
+- see tokens which are used to clone GitLab projects,
+- see the secure variables that are passed to runner.
+
+### Git cloning
+
+Currently the certificates are only used to verify connections between GitLab Runner and GitLab server.
+This doesn't affect git commands (ie. `git clone`).
+You still will see build errors due to TLS validation failure.
+
+To have maximum security for your builds you should configure `GIT_SSL_CAINFO` variable.
+It allows you to define the file containing the certificates to verify the peer with when fetching or pushing over HTTPS
+
+The other options is to disable TLS verification, but as said before this approach is insecure. 
+Add to your `.gitlab-ci.yml` this lines:
+```
+variables:
+  GIT_SSL_NO_VERIFY: "1"
+```

docs/faq/README.md

@@ -29,4 +29,8 @@ project to use *git fetch* from the GitLab CI project settings page.
 
 The [NTFSSecurity](https://ntfssecurity.codeplex.com/) PowerShell module provides
 a *Remove-Item2* method which supports long paths. The Gitlab CI Multi Runner will
-detect it if it is available and automatically make use of it.
+detect it if it is available and automatically make use of it.
\ No newline at end of file
+
+## 4. I'm seeing `x509: certificate signed by unknown authority`
+
+Please [See the self-signed certificates](../configuration/tls-self-signed.md)