OAuth with inbound REST - grant_type=password error

[Colleen]

I am trying to implement OAuth to authenticate external clients who access our custom scripted REST API .

I followed the instructions in the ServiceNow docs > OAuth with inbound REST article to set the OAuth endpoint for external clients, as shown in the screenshot below:

I am using this PowerShell script to make a grant_type=password request to get the access token.

$client_id = '<client id>'

$client_secret = '<client secret>'

$rest_user = '<user name>'

$rest_pw = '<user password>'

$token_url = 'https://<server url>/oauth_token.do'

$content_type = 'application/x-www-form-urlencoded'

$body = "grant_type=password&client_id=$($client_id)&client_secret=$($client_secret)&username=$($rest_user)&password=$($rest_pw)"

$response = Invoke-RestMethod -Method Post -Uri $token_url -ContentType $content_type -Body $body

The Invoke-RestMethod returns the following error:

{"error_description":"access_denied","error":"server_error"}

I have confirmed the username and password credentials by successfully using them with Basic Authentication.

We are currently on Xanadu. I remember previously using the same PowerShell code to successfully get an OAuth access token on an earlier release.

What am I doing wrong? Is there another way to get the OAuth access token?

[Bhuvan · Accepted solution]

@Colleen 

Any specific reason to use Powershell script to get OAuth token ?

Did you try OAuth token request from Postman or REST API Explorer to check you are able to fetch access token and refresh token ?

From Washington release, you can also use Client Credentials based OAuth tokens and would be simpler than grant_type=password OR grant_type=refresh_token

Please refer below thread where I provided more information on this

https://www.servicenow.com/community/itsm-forum/how-to-generate-access-token-from-the-oauth-token-ur...

If this helped to answer your query, please mark it helpful & accept the solution. 

Thanks,

Bhuvan

[M Iftikhar]

Hi @Colleen ,

Please refer to the following community post:
Solved: OAuth 2.0 error access_denied - ServiceNow Community

Try recreating a new application registry.
You can try this as well. It may resolve your issue as well.

Thanks & Regards,
Muhammad Iftikhar
If my response helped, please mark it as the accepted solution so others can benefit as well.

[Bhuvan · Accepted solution]

@Colleen 

Any specific reason to use Powershell script to get OAuth token ?

Did you try OAuth token request from Postman or REST API Explorer to check you are able to fetch access token and refresh token ?

From Washington release, you can also use Client Credentials based OAuth tokens and would be simpler than grant_type=password OR grant_type=refresh_token

Please refer below thread where I provided more information on this

https://www.servicenow.com/community/itsm-forum/how-to-generate-access-token-from-the-oauth-token-ur...

If this helped to answer your query, please mark it helpful & accept the solution. 

Thanks,

Bhuvan

[Bhuvan]

@Colleen 

Did you get a chance to review this as I believe the information provided should answer your question.

If my response helped to guide you or answer your query, please mark it helpful & accept the solution.

Thanks,

Bhuvan

[Colleen]

Hi Bhuvan

I want to use OAuth to authenticate a scripted REST API to enable an external client to generate tickets in ServiceNow.  I was trying to use the password grant_type because I want the tickets to be associated with the specified user.  As far as I understand the client_credentials grant type is not associated with a user context.