Adding some standard OpenID Connect providers (Google, Facebook) (WIP):

* refactoring, to allow several OIDC singletons
* settings for google and facebook
* backend code

server/lib/diagnostic/external-auth-oidc.ts

@@ -0,0 +1,63 @@
+import type { RegisterServerOptions } from '@peertube/peertube-types'
+import { newResult, TestResult } from './utils'
+import { ExternalAuthOIDC, ExternalAuthOIDCType } from '../external-auth/oidc'
+
+export async function diagExternalAuthOIDC (
+  test: string,
+  _options: RegisterServerOptions,
+  singletonType: ExternalAuthOIDCType,
+  next: TestResult['next']
+): Promise<TestResult> {
+  const result = newResult(test)
+  result.label = 'Test External Auth OIDC: ' + singletonType
+  result.next = next
+
+  try {
+    const oidc = ExternalAuthOIDC.singleton(singletonType)
+
+    if (oidc.isDisabledBySettings()) {
+      result.ok = true
+      result.messages.push('Feature disabled in plugins settings.')
+      return result
+    }
+
+    result.messages.push('Discovery URL: ' + (oidc.getDiscoveryUrl() ?? 'undefined'))
+
+    const oidcErrors = await oidc.check()
+    if (oidcErrors.length) {
+      result.messages.push({
+        level: 'error',
+        message: 'The ExternalAuthOIDC singleton got some errors:'
+      })
+      for (const oidcError of oidcErrors) {
+        result.messages.push({
+          level: 'error',
+          message: oidcError
+        })
+      }
+      return result
+    }
+  } catch (err) {
+    result.messages.push({
+      level: 'error',
+      message: 'Error while retrieving the ExternalAuthOIDC singleton:' + (err as string)
+    })
+    return result
+  }
+
+  const oidc = ExternalAuthOIDC.singleton(singletonType)
+  const oidcClient = await oidc.load()
+  if (oidcClient) {
+    result.messages.push('Discovery URL loaded: ' + JSON.stringify(oidcClient.issuer.metadata))
+  } else {
+    result.messages.push({
+      level: 'error',
+      message: 'Failed to load the Discovery URL.'
+    })
+    return result
+  }
+
+  result.ok = true
+  result.messages.push('Configuration OK.')
+  return result
+}