diff --git a/src/scripts/tools/add_tools.ps1 b/src/scripts/tools/add_tools.ps1
index cfe28fe9..46c99757 100644
--- a/src/scripts/tools/add_tools.ps1
+++ b/src/scripts/tools/add_tools.ps1
@@ -28,6 +28,39 @@ Function Edit-ComposerConfig() {
   Set-ComposerAuth
 }
 
+# Function to merge auth.json fragments.
+Function Get-MergedAuthJson {
+  [CmdletBinding()]
+  param(
+    [Parameter(Mandatory)][string[]] $ComposerAuth
+  )
+  if (Test-Path $composer_home\auth.json) {
+    try {
+      $existing = Get-Content $composer_home\auth.json -Raw | ConvertFrom-Json
+    } catch {
+      $existing = [PSCustomObject]@{}
+    }
+  } else {
+    $existing = [PSCustomObject]@{}
+  }
+  foreach ($fragment in $ComposerAuth) {
+    $piece = ('{' + $fragment + '}') | ConvertFrom-Json
+    foreach ($prop in $piece.PSObject.Properties) {
+      if ($prop.Name -eq 'http-basic') {
+        if (-not $existing.'http-basic') {
+          $existing | Add-Member -MemberType NoteProperty -Name 'http-basic' -Value ([PSCustomObject]@{}) -Force
+        }
+        foreach ($domainProp in $prop.Value.PSObject.Properties) {
+          $existing.'http-basic' | Add-Member -MemberType NoteProperty -Name $domainProp.Name -Value $domainProp.Value -Force
+        }
+      } else {
+        $existing | Add-Member -MemberType NoteProperty -Name $prop.Name -Value $prop.Value -Force
+      }
+    }
+  }
+  return $existing | ConvertTo-Json -Depth 5
+}
+
 # Function to setup authentication in composer.
 Function Set-ComposerAuth() {
   if(Test-Path env:COMPOSER_AUTH_JSON) {
@@ -48,7 +81,7 @@ Function Set-ComposerAuth() {
     $composer_auth += '"github-oauth": {"github.com": "' + $env:GITHUB_TOKEN + '"}'
   }
   if($composer_auth.length) {
-    Add-Env COMPOSER_AUTH ('{' + ($composer_auth -join ',') + '}')
+    Set-Content -Path $composer_home\auth.json -Value (Get-MergedAuthJson $composer_auth)
   }
 }
 
diff --git a/src/scripts/tools/add_tools.sh b/src/scripts/tools/add_tools.sh
index 99a736f6..7cd6524b 100644
--- a/src/scripts/tools/add_tools.sh
+++ b/src/scripts/tools/add_tools.sh
@@ -46,6 +46,25 @@ configure_composer() {
   set_composer_auth
 }
 
+# Function to merge auth.json fragments.
+get_merged_auth_json() {
+  local auth_file="$composer_home/auth.json"
+  local merged
+  [[ -f "$auth_file" ]] && merged=$(<"$auth_file") || merged='{}'
+  for frag in "$@"; do
+    local obj="{$frag}"
+    merged=$(jq -n --argjson b "$merged" --argjson n "$obj" '
+      if $n|has("http-basic") then
+        (($b["http-basic"]//{}) + $n["http-basic"]) as $hb
+        | ($b + $n) | .["http-basic"] = $hb
+      else
+        $b + $n
+      end
+    ')
+  done
+  printf '%s' "$merged"
+}
+
 # Function to setup authentication in composer.
 set_composer_auth() {
   if [ -n "$COMPOSER_AUTH_JSON" ]; then
@@ -63,7 +82,7 @@ set_composer_auth() {
     composer_auth+=( '"github-oauth": {"github.com": "'"${GITHUB_TOKEN:-$COMPOSER_TOKEN}"'"}' )
   fi
   if ((${#composer_auth[@]})); then
-    add_env COMPOSER_AUTH "{$(IFS=$','; echo "${composer_auth[*]}")}"
+    get_merged_auth_json "${composer_auth[@]}" | tee "$composer_home/auth.json" >/dev/null
   fi
 }