Add a ruletype that checks for the presence of a file header

rule-types/common/file_header.test.yaml

@@ -0,0 +1,43 @@
+tests:
+  - name: "Specific file has a header"
+    def:
+      filter: LICENSE
+      header: |
+        # SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+        # SPDX-License-Identifier: Apache-2.0
+    params: {}
+    expect: "pass"
+    git:
+      repo_base: test_1
+  - name: "Specific file doesn't have a header"
+    def:
+      filter: LICENSE
+      header: |
+        # SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+        # SPDX-License-Identifier: Apache-2.0
+    params: {}
+    expect: "fail"
+    git:
+      repo_base: test_2
+  - name: "All go files have a header"
+    def:
+      filter: LICENSE
+      header: |
+        # SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+        # SPDX-License-Identifier: Apache-2.0
+    params: {}
+    expect: "pass"
+    filter: "^.*\\.go$"
+    git:
+      repo_base: test_1
+  - name: "Not all go files have a header"
+    def:
+      filter: LICENSE
+      header: |
+        # SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+        # SPDX-License-Identifier: Apache-2.0
+    params: {}
+    expect: "fail"
+    filter: "^.*\\.go$"
+    git:
+      repo_base: test_2

rule-types/common/file_header.testdata/test_1/LICENSE

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+# SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+# SPDX-License-Identifier: Apache-2.0
+
+Test file for license header

rule-types/common/file_header.testdata/test_1/file.go

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+// SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+// SPDX-License-Identifier: Apache-2.0
+package test_1

rule-types/common/file_header.testdata/test_1/file_2.go

@@ -0,0 +1,3 @@
+// SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+// SPDX-License-Identifier: Apache-2.0
+package test_1

rule-types/common/file_header.testdata/test_2/LICENSE

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+# Another header
+
+Test file for license header

rule-types/common/file_header.testdata/test_2/file.go

@@ -0,0 +1,3 @@
+// SPDX-FileCopyrightText: Copyright 2023 The Minder Authors
+// SPDX-License-Identifier: Apache-2.0
+package test_1

rule-types/common/file_header.testdata/test_2/file_2.go

@@ -0,0 +1 @@
+package test_1

rule-types/common/file_header.yaml

@@ -0,0 +1,73 @@
+---
+version: v1
+release_phase: alpha
+type: rule-type
+name: file_header
+display_name: Checks for the presence of a header in a file
+short_failure_message: File does not contain the expected header
+severity:
+  value: low
+context: {}
+description: |
+  Checks for the presence of a header in a file.
+guidance: |
+  Check if the file contains the expected header. 
+
+  This rule is useful for enforcing the presence of a header in a file, such as license headers, code of conduct,
+  or other important information that should be present in the beginning of the file.
+def:
+  in_entity: repository
+  rule_schema:
+    type: object
+    properties:
+      filter:
+        type: string
+        description: |
+          The filter is a regular expression that is used to filter the files that should be checked for the header.
+
+          For example, if you want to check all files with the extension `.yml`, you can use the following regex `^.*\.yml$`.
+
+          If you want to check a specific file, you can use the file name as the filter. For example, `main.go`.
+      header:
+        type: string
+        description: |
+          The header to check for in the file.
+
+          This is the expected content that should be present in the beginning of the file.
+    required:
+      - filter
+      - header
+  ingest:
+    type: git
+    git:
+  eval:
+    type: rego
+    rego:
+      type: constraints
+      def: |
+        package minder
+
+        import future.keywords.in
+        import future.keywords.if
+
+        violations[{"msg": msg}] if {
+          # Walk all files in the repo
+          files_in_repo := file.walk(".")
+
+          some current_file in files_in_repo
+
+          # Filter files based on the regex in filter
+          regex.match(input.profile.filter, current_file)
+
+          # Read the file
+          file_content := file.read(current_file)
+
+          # Check if the file contains the expected header
+          not startswith(file_content, input.profile.header)
+
+          msg := sprintf("File does not contain the expected header: %s", [current_file])
+        }
+  # Defines the configuration for alerting on the rule
+  alert:
+    type: security_advisory
+    security_advisory: {}