Rework OAuth sources (#244)

This change request includes two different things to improve OAuth source handling:

- Allow multiple OAuth source configuration (Fixes: #191)
- Support reading sensitive OAuth configuration data from Kubernetes secrets (Closes: #242)

⚠️ BREAKING ⚠️
---

Users need to migrate their `gitea.oauth` configuration.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/244
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Reviewed-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-committed-by: justusbunsi <justusbunsi@noreply.gitea.io>

templates/_helpers.tpl

@@ -138,9 +138,20 @@ app.kubernetes.io/instance: {{ .Release.Name }}
 {{- end -}}
 
 {{- define "gitea.oauth_settings" -}}
-{{- range $key, $val := .Values.gitea.oauth -}}
-{{- if ne $key "enabled" -}}
-{{- printf "--%s %s " ($key | kebabcase) ($val | squote) -}}
+{{- $idx := index . 0 }}
+{{- $values := index . 1 }}
+
+{{- if not (hasKey $values "key") -}}
+{{- $_ := set $values "key" (printf "${GITEA_OAUTH_KEY_%d}" $idx) -}}
+{{- end -}}
+
+{{- if not (hasKey $values "secret") -}}
+{{- $_ := set $values "secret" (printf "${GITEA_OAUTH_SECRET_%d}" $idx) -}}
+{{- end -}}
+
+{{- range $key, $val := $values -}}
+{{- if and (ne $key "enabled") (ne $key "existingSecret") -}}
+{{- printf "--%s %s " ($key | kebabcase) ($val | quote) -}}
 {{- end -}}
 {{- end -}}
 {{- end -}}