WebApi returning (401) Unauthorized error

Question

Hi All, 
 I have created a WebApi in Appin with Post which is getting invoked by another non-appian application. But the other application is getting 
 The remote server returned an error: (401) Unauthorized error. I tried to test using powershell but getting invalid username\password error there. 
 Please find the request body captured in the log below. I have removed the request body due to company security policy. 
 { "Connection": "Keep-Alive", "Content-Length": "633", "Content-Type": "application/json", "Authorization": "Basic d3N1c2VyOndzcGFzc3dvcmQx", "Host": "rmsstgintweb1", "User-Agent": "Mozilla/5.0 (Windows NT; Windows NT 6.1; en-US) WindowsPowerShell/5.0.10586.117", "Body": "" } 
 Below are the things I checked. 
 1. I have created third party credential in Admin console and the other system is using the same credential while invoking appin webapi 
 2. I have created a system admin user account for the webservice user cedential 
 3. Checked webapi and process model security. They looked fine. 
 Please let me know what I am missing? Do I need to install any base64 plugin for this? Any help\pointer is appreciated. Thanks in advance

Dan Lluhi · Answer

Hi, please make sure you are using HTTP Basic authentication with preemptive authentication. From the documentation ( docs.appian.com/.../Web_APIs.html 
 
"If you wish to invoke an Appian Web API from another system, you must use HTTP basic authentication. HTTP basic authentication for Appian Web APIs requires preemptive authentication as unauthorized requests will not prompt clients for credentials with a 401 status code." 
 
Thanks, 
Dan

sureshg57 · Answer

HI 
 
 401 unauthorised error is more self explanatory and it direct you attention to the user authorisation. 
 
2 things can cause this 
1. first check the appian user credential you are passing in request is correct. if this is correct then 
2. check if the user has access to invoke webAPI. The user should have at least Viewer level of access to webAPI object. 
 
regards 
suresh

aloks0189 · Answer

Hi subhashreel0001 you can try following steps to resolve this issue: 
 
1. Make sure, the client is using Third Party Credentials for HTTP Basic Authentication Mode only, also make sure that, preemptive should 
be set to true 
2. If after following Step-1, still the same issue continues, then add the clients IP into Cors Settings under Admin Console 
 
Hope this will help you to resolve 401 issue.