docs(bitbucket-pipelines): authenticated registries

lib/modules/manager/bitbucket-pipelines/readme.md

@@ -1,3 +1,51 @@
 Extracts dependencies from Bitbucket Pipelines config files.
 
 If you need to change the versioning format, read the [versioning](https://docs.renovatebot.com/modules/versioning/) documentation to learn more.
+
+### Using private build images
+
+Bitbucket Pipelines supports using an authenticated Docker registry, including self-hosted private registries, Docker Hub, Amazon ECR and Google GCR.
+
+More details can be found on the Atlassian [Bitbucket Pipeline documentation](https://support.atlassian.com/bitbucket-cloud/docs/use-docker-images-as-build-environments) site
+
+The following `regexManager` configuration can be used for authenticated Docker Hub or private registries.
+You'll need to change this example config if you're using Amazon ECR or Google GCR.
+
+```json
+{
+  "regexManagers": [
+    {
+      "matchManagers": ["bitbucket-pipelines"],
+      "matchStrings": [
+        "\\s*-?\\s?image:\\s*\\n\\s+name:\\s+\"?(?<depName>[a-z/.-]+)(?::(?<currentValue>[a-z0-9.-]+))?(?:@(?<currentDigest>sha256:[a-f0-9]+))?"
+      ],
+      "datasourceTemplate": "docker",
+      "versioningTemplate": "docker"
+    }
+  ]
+}
+```
+
+### Replacing unauthenticated with authenticated registries
+
+With the [regex manager](https://docs.renovatebot.com/modules/manager/regex/) you can configure Renovate to assist with migrating your Bitbucket Pipelines from unauthenticated registries to authenticated registries.
+
+For example:
+
+```json
+{
+  "regexManagers": [
+    {
+      "description": "Bitbucket Pipelines: migrate from unauthenticated to authenticated registry",
+      "fileMatch": ["(^|\\/|\\.)bitbucket-pipelines.ya?ml$"],
+      "matchStringsStrategy": "combination",
+      "matchStrings": [
+        "\\s*image:\\s*(?<depName>[a-z-]+)(?::(?<currentValue>[a-z0-9.-]+))?(?:@(?<currentDigest>sha256:[a-f0-9]+))?",
+        "\\s*image:\\s*\\n\\s*name:\\s*(?<depName>[a-z-]+)(?::(?<currentValue>[a-z0-9.-]+))?(?:@(?<currentDigest>sha256:[a-f0-9]+))?\\n\\s*username:\\s*\\$SOME_USER\\n\\s*password:\\s*\\$SOME_PASSWORD"
+      ],
+      "datasourceTemplate": "docker",
+      "autoReplaceStringTemplate": "image:\n  name: {{{packageName}}}{{#if newValue}}:{{{newValue}}}{{/if}}{{#if newDigest}}@{{{newDigest}}}{{/if}}\n  username: $SOME_USER\n  password: $SOME_PASSWORD"
+    }
+  ]
+}
+```