feat: Add function to decode JWT tokens

functions/utils/convert.sh

@@ -1,33 +1,3 @@
-decode_base64() {
-  local input="$1"
-  local decoded="$input"
-  local temp
-
-  if [ -z "$input" ]; then
-    echo "Error: input is empty." >&2
-    return 1
-  fi
-
-  while true; do
-    if temp=$(echo -n "$decoded" | base64 -d 2>/dev/null) && [ -n "$temp" ]; then
-      if [ "$temp" = "$decoded" ]; then
-        break
-      fi
-
-      if echo -n "$temp" | LC_ALL=C grep -q '[^[:print:][:space:]]'; then
-        break
-      fi
-
-      decoded="$temp"
-    else
-      break
-    fi
-  done
-
-  printf '%s' "$decoded"
-  printf '\n'
-}
-
 # convert myVar to my-var
 convert_camel_case_to_kebab_case() {
   echo "$1" | sed -r 's/([a-z0-9])([A-Z])/\1-\2/g' | tr '[:upper:]' '[:lower:]'

functions/utils/decode.sh

@@ -0,0 +1,75 @@
+decode_base64_url() {
+  # Replace URL-safe characters with standard Base64 characters.
+  local input=$1
+  input=${input//-/+}
+  input=${input//_/\/}
+
+  # Pad with '=' if necessary
+  local mod4=$((${#input} % 4))
+  if ((mod4 != 0)); then
+    input="${input}$(printf '%0.s=' $(seq $((4 - mod4))))"
+  fi
+
+  echo "$input" | base64 -d 2>/dev/null
+}
+
+decode_jwt() {
+  if [[ -z "$1" ]]; then
+    echo -e "Usage: decode_jwt <jwt>\nSplits and decodes a JSON Web Token."
+    return
+  fi
+
+  local jwt=$1
+  local delimiter_count
+
+  delimiter_count=$(grep -o '\.' <<<"$jwt" | wc -l)
+  if [[ "$delimiter_count" -ne 2 ]]; then
+    echo "Error: Invalid JWT format. A JWT must contain exactly two dots."
+    return 1
+  fi
+
+  IFS='.' read -r header payload signature <<<"$jwt"
+  if [[ -z "$header" || -z "$payload" || -z "$signature" ]]; then
+    echo "Error: JWT parts cannot be empty."
+    return 1
+  fi
+
+  echo "Header:"
+  decode_base64_url "$header" | jq .
+
+  echo "Payload:"
+  decode_base64_url "$payload" | jq .
+
+  echo "Signature (Base64Url):"
+  echo "$signature"
+}
+
+decode_base64() {
+  local input="$1"
+  local decoded="$input"
+  local temp
+
+  if [ -z "$input" ]; then
+    echo "Error: input is empty." >&2
+    return 1
+  fi
+
+  while true; do
+    if temp=$(echo -n "$decoded" | base64 -d 2>/dev/null) && [ -n "$temp" ]; then
+      if [ "$temp" = "$decoded" ]; then
+        break
+      fi
+
+      if echo -n "$temp" | LC_ALL=C grep -q '[^[:print:][:space:]]'; then
+        break
+      fi
+
+      decoded="$temp"
+    else
+      break
+    fi
+  done
+
+  printf '%s' "$decoded"
+  printf '\n'
+}

tests/functions/utils/test_convert.bats

@@ -2,6 +2,7 @@
 
 repo_root=$(git rev-parse --show-toplevel)
 
+load "$repo_root/functions/utils/decode.sh"
 load "$repo_root/functions/utils/convert.sh"
 
 @test "decode_base64" {