Support GitHub-style (sha256 signature) git hooks

Author: sealexan

src/main/kotlin/ch/uzh/ifi/access/controller/CourseController.kt

@@ -45,10 +45,16 @@ class WebhooksController(
     private val logger = KotlinLogging.logger {}
 
     @PostMapping("/courses/{course}/update/gitlab")
-    fun updateCourse(@PathVariable("course") course: String,
+    fun hookGitlab(@PathVariable("course") course: String,
                      @RequestHeader("X-Gitlab-Token") secret: String) {
-        logger.debug { "webhook triggered for $course"}
-        courseService.webhookUpdateCourse(course, secret)
+        logger.debug { "webhook (secret) triggered for $course"}
+        courseService.webhookUpdateWithSecret(course, secret)
+    }
+    @PostMapping("/courses/{course}/update/github")
+    fun hookGithub(@PathVariable("course") course: String,
+                     @RequestHeader("X-Hub-Signature-256") signature: String) {
+        logger.debug { "webhook (signature) triggered for $course"}
+        courseService.webhookUpdateWithSignature(course, signature.substringAfter("sha256="))
     }
 
 }

src/main/kotlin/ch/uzh/ifi/access/service/CourseService.kt

@@ -35,6 +35,7 @@ import java.nio.charset.Charset
 import java.nio.file.Files
 import java.nio.file.NoSuchFileException
 import java.nio.file.Path
+import java.security.MessageDigest
 import java.time.LocalDateTime
 import java.time.format.DateTimeFormatter
 import java.util.*
@@ -43,6 +44,7 @@ import java.util.concurrent.TimeUnit
 import java.util.function.Consumer
 import java.util.stream.Collectors
 import java.util.stream.Stream
+import kotlin.math.sign
 
 @Service
 class CourseServiceForCaching(
@@ -554,10 +556,27 @@ fi
     }
 
     @Transactional
-    fun webhookUpdateCourse(courseSlug: String, secret: String): Course? {
+    fun webhookUpdateWithSecret(courseSlug: String, secret: String?): Course? {
         val existingCourse = getCourseBySlug(courseSlug)
-        if (existingCourse.webhookSecret != null && existingCourse.webhookSecret == secret) {
-            return updateCourse(courseSlug)
+        if (existingCourse.webhookSecret != null && secret != null) {
+            if (existingCourse.webhookSecret == secret) {
+                return updateCourse(courseSlug)
+            }
+        }
+        logger.debug { "Provided webhook secret does not match secret of course $courseSlug"}
+        throw ResponseStatusException(HttpStatus.FORBIDDEN)
+    }
+
+    fun webhookUpdateWithSignature(courseSlug: String, signature: String?): Course? {
+        val existingCourse = getCourseBySlug(courseSlug)
+        if (existingCourse.webhookSecret != null && signature != null) {
+            val expected = MessageDigest.getInstance("SHA-256")
+                .digest(existingCourse.webhookSecret!!.toByteArray())
+                .fold("") { str, it -> str + "%02x".format(it) }
+            logger.info{"Expected: ${expected} based on secret ${existingCourse.webhookSecret}, actual: ${signature}"}
+            if (expected == signature) {
+                return updateCourse(courseSlug)
+            }
         }
         logger.debug { "Provided webhook secret does not match secret of course $courseSlug"}
         throw ResponseStatusException(HttpStatus.FORBIDDEN)