3 files changed, 44 insertions, 5 deletions
diff --git a/src/git-source-provider.ts b/src/git-source-provider.ts
index 89c16b5..25fba04 100644
--- a/src/git-source-provider.ts
+++ b/src/git-source-provider.ts
@@ -19,6 +19,17 @@ export async function getSource(settings: IGitSourceSettings): Promise<void> {
   )
   const repositoryUrl = urlHelper.getFetchUrl(settings)
 
+  // Determine the default branch
+  if (!settings.ref && !settings.commit) {
+    core.startGroup('Determining the default branch')
+    settings.ref = await githubApiHelper.getDefaultBranch(
+      settings.authToken,
+      settings.repositoryOwner,
+      settings.repositoryName
+    )
+    core.endGroup()
+  }
+
   // Remove conflicting file path
   if (fsHelper.fileExistsSync(settings.repositoryPath)) {
     await io.rmRF(settings.repositoryPath)
diff --git a/src/github-api-helper.ts b/src/github-api-helper.ts
index e559c45..7a09638 100644
--- a/src/github-api-helper.ts
+++ b/src/github-api-helper.ts
@@ -67,6 +67,38 @@ export async function downloadRepository(
   io.rmRF(extractPath)
 }
 
+/**
+ * Looks up the default branch name
+ */
+export async function getDefaultBranch(
+  authToken: string,
+  owner: string,
+  repo: string
+): Promise<string> {
+  return await retryHelper.execute(async () => {
+    core.info('Retrieving the default branch name')
+    const octokit = new github.GitHub(authToken)
+    const response = await octokit.repos.get({owner, repo})
+    if (response.status != 200) {
+      throw new Error(
+        `Unexpected response from GitHub API. Status: ${response.status}, Data: ${response.data}`
+      )
+    }
+
+    // Print the default branch
+    let result = response.data.default_branch
+    core.info(`Default branch '${result}'`)
+    assert.ok(result, 'default_branch cannot be empty')
+
+    // Prefix with 'refs/heads'
+    if (!result.startsWith('refs/')) {
+      result = `refs/heads/${result}`
+    }
+
+    return result
+  })
+}
+
 async function downloadArchive(
   authToken: string,
   owner: string,
diff --git a/src/input-helper.ts b/src/input-helper.ts
index 11a1ab6..eabb9e0 100644
--- a/src/input-helper.ts
+++ b/src/input-helper.ts
@@ -68,10 +68,6 @@ export function getInputs(): IGitSourceSettings {
         result.ref = `refs/heads/${result.ref}`
       }
     }
-
-    if (!result.ref && !result.commit) {
-      result.ref = 'refs/heads/master'
-    }
   }
   // SHA?
   else if (result.ref.match(/^[0-9a-fA-F]{40}$/)) {
@@ -110,7 +106,7 @@ export function getInputs(): IGitSourceSettings {
   core.debug(`recursive submodules = ${result.nestedSubmodules}`)
 
   // Auth token
-  result.authToken = core.getInput('token')
+  result.authToken = core.getInput('token', {required: true})
 
   // SSH
   result.sshKey = core.getInput('ssh-key')