doc: added secret description to architecture.md.

doc/architecture.md

@@ -136,3 +136,11 @@ string. This string is validated against the platform's authentication API. If t
 the User's GitLab profile to retrieve their *GitLab User ID*. Based on the *GitLab User ID* we generate a JWT, which is
 returned to the *Dashboard* as a `SET_COOKIE`. Based on this cookie we can display user specific content, i.e., when the
 user visits the *Dashboard* for a project they own. In this case we display more detailed tool results.
+
+### Secrets
+
+To function correctly, our application needs to be started with a set of secret values. On the one hand to access
+existing APIs protected by API keys, or on the other hand to set the passwords and API keys for our own API.
+All relevant secrets are defined as kubernetes secrets in our cluster. Our CI/CD builds the *Data-Provider* and deploys
+it to the kubernetes cluster. The cluster access is configured through CI/CD variables in GitLab's project settings.
+The *Data-Provider* loads the secrets through environment variables.