Add support for service accounts | Resolve #122

* Add guide in readme on how to generate

* Add -sa/--service-account flag

* access tokens created by sa will be saved in config, when the sa is given, then it will try to reuse the access token if valid

README.md

@@ -50,6 +50,7 @@
   - [Updation](#updation)
 - [Usage](#usage)
   - [Generating Oauth Credentials](#generating-oauth-credentials)
+  - [Generating service account credentials](#generating-service-account-credentials)
   - [Enable Drive API](#enable-drive-api)
   - [First Run](#first-run)
   - [Config file](#config)
@@ -296,10 +297,14 @@ There are two methods:
 
 ## Usage
 
-First, we need to obtain our oauth credentials, here's how to do it:
+First, we have to authenticate.
+
+There are two ways to authenticate, oauth credentials or service accounts. Use any one.
 
 ### Generating Oauth Credentials
 
+To obtain oauth credentials, follow below steps:
+
 - Follow [Enable Drive API](#enable-drive-api) section.
 - Open [google console](https://console.developers.google.com/).
 - Click on "Credentials".
@@ -311,6 +316,24 @@ First, we need to obtain our oauth credentials, here's how to do it:
 
 Now, we have obtained our credentials, move to the [First run](#first-run) section to use those credentials:
 
+### Generating service account credentials
+
+To obtain service account credentials, follow below steps:
+
+- Follow [Enable Drive API](#enable-drive-api) section.
+- Open [google console](https://console.developers.google.com/).
+- Click on "Credentials".
+- Click "Create credentials" and select "Service account".
+- Provide name for service account and click on create. If successful, it should be on step 2.
+- Now tap on role and select owner. Click on continue. If successful, it should be on step 3.
+- Click on done.
+- Now click on manage service accounts.
+- Click on the service account name you created.
+- Click on add key, then tap on create new key. Choose json and tap on create.
+- If successful, a file should download in the .json format.
+
+Now, we have obtained our service account json, move to the [First run](#first-run) section to use those credentials:
+
 ### Enable Drive API
 
 - Log into google developer console at [google console](https://console.developers.google.com/).
@@ -331,28 +354,46 @@ By this, a side bar is opened. At there, select "API & Services" -> "Library". A
 
 [Go back to oauth credentials setup](#generating-oauth-credentials)
 
+[Go back to service account generation](#generating-service-account-credentials)
+
 ### First Run
 
+On first run, there are two possibilities, either using oauth credentials or service account credentials.
+
+#### For Oauth
+
 On first run, the script asks for all the required credentials, which we have obtained in the previous section.
 
 Execute the script: `gupload filename`
 
 Now, it will ask for following credentials:
 
-**Client ID:** Copy and paste from credentials.json
+- **Client ID:** Copy and paste from credentials.json
 
-**Client Secret:** Copy and paste from credentials.json
+- **Client Secret:** Copy and paste from credentials.json
 
-**Refresh Token:** If you have previously generated a refresh token authenticated to your account, then enter it, otherwise leave blank.
+- **Refresh Token:** If you have previously generated a refresh token authenticated to your account, then enter it, otherwise leave blank.
 If you don't have refresh token, script outputs a URL on the terminal script, open that url in a web browser and tap on allow. Copy the code and paste in the terminal.
 
-**Root Folder:** Gdrive folder url/id from your account which you want to set as root folder. You can leave it blank and it takes `root` folder as default.
+- **Root Folder:** Gdrive folder url/id from your account which you want to set as root folder. You can leave it blank and it takes `root` folder as default.
 
 If everything went fine, all the required credentials have been set, read the next section on how to upload a file/folder.
 
+#### For service accounts
+
+For using service account, use `-sa | --service-account` flag.
+
+Execute the script: `gupload filename -sa "service account json file path"`
+
+Note: For service accounts it is necessary to use the `-sa | --service-account` flag everytime.
+
+For more info, see `-sa | --service-account` flag in [Upload Script Custom Flags](#upload-script-custom-flags).
+
 ### Config
 
-After first run, the credentials are saved in config file. By default, the config file is `${HOME}/.googledrive.conf`.
+After first run, if oauth credentials are used, then credentials are saved in config file, otherwise for service accounts it is necessary to use the `-sa | --service-account` flag everytime.
+
+By default, the config file is `${HOME}/.googledrive.conf`.
 
 To change the default config file or use a different one temporarily, see `-z / --config` custom in [Upload Script Custom Flags](#upload-script-custom-flags).
 
@@ -410,6 +451,14 @@ Apart from basic usage, this script provides many flags for custom usecases, lik
 
 These are the custom flags that are currently implemented:
 
+-   <strong>--sa | --service-accounts 'service account json file path'</strong>
+
+    Use a service account. Should be in proper json format.
+
+    To generate service accounts, see [service account generation](#generating-service-account-credentials) section.
+
+    ---
+
 -   <strong>-z | --config</strong>
 
     Override default config file with custom config file.

bash/drive-utils.bash

@@ -186,11 +186,22 @@ _extract_id() {
 # Result: Update access_token and expiry else print error
 ###################################################
 _get_access_token_and_update() {
-    RESPONSE="${1:-$(curl --compressed -s -X POST --data "client_id=${CLIENT_ID}&client_secret=${CLIENT_SECRET}&refresh_token=${REFRESH_TOKEN}&grant_type=refresh_token" "${TOKEN_URL}")}" || :
+    case "${1:?Error: sa or normal}" in
+        normal)
+            RESPONSE="${2:-$(curl --compressed -s -X POST --data "client_id=${CLIENT_ID}&client_secret=${CLIENT_SECRET}&refresh_token=${REFRESH_TOKEN}&grant_type=refresh_token" "${TOKEN_URL}")}" || :
+            ;;
+        sa)
+            declare assertion_data="${2:?2lError: Missing assertion data.}"
+            RESPONSE="$(curl --compressed -s --data "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&assertion=${assertion_data}" "${TOKEN_URL}")" || :
+            # sa token jsons are not pretty printed
+            RESPONSE="${RESPONSE//,\"/$'\n'\"}"
+            ;;
+    esac
+
     if ACCESS_TOKEN="$(_json_value access_token 1 1 <<< "${RESPONSE}")"; then
         ACCESS_TOKEN_EXPIRY="$(($(printf "%(%s)T\\n" "-1") + $(_json_value expires_in 1 1 <<< "${RESPONSE}") - 1))"
-        _update_config ACCESS_TOKEN "${ACCESS_TOKEN}" "${CONFIG}"
-        _update_config ACCESS_TOKEN_EXPIRY "${ACCESS_TOKEN_EXPIRY}" "${CONFIG}"
+        _update_config "${SERVICE_ACCOUNT:+${SERVICE_ACCOUNT}_}ACCESS_TOKEN" "${ACCESS_TOKEN}" "${CONFIG}"
+        _update_config "${SERVICE_ACCOUNT:+${SERVICE_ACCOUNT}_}ACCESS_TOKEN_EXPIRY" "${ACCESS_TOKEN_EXPIRY}" "${CONFIG}"
     else
         "${QUIET:-_print_center}" "justify" "Error: Something went wrong" ", printing error." 1>&2
         printf "%s\n" "${RESPONSE}" 1>&2

bash/google-oauth2.bash

@@ -123,7 +123,7 @@ if [[ ${1} = create ]]; then
 elif [[ ${1} = refresh ]]; then
     if [[ -n ${REFRESH_TOKEN} ]]; then
         _print_center "justify" "Required credentials set." "="
-        { _get_access_token_and_update && _clear_line 1; } || return 1
+        { _get_access_token_and_update normal && _clear_line 1; } || return 1
         printf "Access Token: %s\n" "${ACCESS_TOKEN}"
     else
         "${QUIET:-_print_center}" "normal" "Refresh Token not set" ", use ${0##*/} create to generate one." "="