Postman error: "Unable to verify the first certificate" when try to get from my .net core API

Question

I have my brand new .NET Core service with API and I want to get list of items inside it. It's hosted on localhost and I always have this error:

16 ms
Warning: Unable to verify the first certificate
Network
Request Headers
User-Agent: PostmanRuntime/7.26.8
Accept: */*
Postman-Token: e64e10c3-8e3a-4b47-9427-d994e2bdc9fd
Host: localhost:44397
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Request Body
Response Headers
Transfer-Encoding: chunked
Server: Microsoft-IIS/10.0
X-Powered-By: ASP.NET
Date: Tue, 19 Ja

n 2021 14:06:14 GMT
Response Body

How to fix it? I disabled/enabled SSL certification but it no helps.

Subchaser

forums.ivanti.com/s/article/… – Maclaine

@RomanRyzhiy i tried both options but i can't understand option I, just don't understand how to export certificate, i don't have anything mentioned in instruction in that mmc.exe – Subchaser

I have suddenly started to get this on my local machine too. In my case all of the settings in the answer below are turned off. – Kimbra

Same issue during development localhost https .net. – Battlefield

Solved! Postman Version 9.14.6 pops up to disable SSL. On disabling Working fine – Felixfeliza

any solutions ? i have disabled all ssl but still same issue – Democratic

Answer 1

There are 3 places to disable ssl verification:

1. Request level: make sure it is off

2. Global level: (Request level will have precedence)

3. Remove client and CA certificate, turn it to off :

Sik

Everywhere you pointed i have turned off SSL certificate and error still showing up, i don't understand why people giving -1 when somebody have uncommon issue. – Subchaser

ANy luck, even iam also facing the same issue. even after turn off the ssl certificate – Shoulders

Is there a example website that you can reproduce this issue – Sik

I completed all 3 of these and am still getting the same error – Cardiovascular

I resolved this problem by removing the whitespace at the end of a url. copy/paste really got me – Pickwickian

I have the same issue even after following the 3 steps – Latish

Answer 2

May be you forgotten to add this lines into Program.cs,

app.UseAuthentication();
app.UseAuthorization();

Asmara

This fixed my problem. And also got rid of my missing aud claim error. – Quartz

Answer 3

First, your OS (Windows, Mac, Linux) must trust this certificate.

Then, in Postman, go to Settings > Certificates, and enable CA certification, then select the same trusted certificate.

Longawa

Answer 4

I had the same issue with the Postman unable to verify the first certificate. The same localhost endpoint worked within a browser, but not in Postman while running in debug in VS. In my case re-installing IIS Express fixed the problem.

Salmon

Answer 5

upload the root ca of the certificate issuer in postman and it will work

Eastwood

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. – Calisa

I has this issue with R3 (Let's Encrypt) certificate. To solve that, go to Settings -> Certificates -> CA Certificates and add the Root CA file. In my case it was ca.cer. Despite asking for a .pem file, I just sent the ca.cer file and it worked fine. – Wallah

Answer 6

For me the issue was that my controller was annotated with a router template [Route("api/[controller]")] but my endpoints were not. Adding endpoint annotations worked:

[HttpGet("get")]
public string Get()
{
    return "get";
}

Smoothtongued

At the very least, I believe HttpGet("get")] is missing a [. /shrug – Incised

Answer 7

I solved the issue for me by recognizing, that my CA certificate file ending on .cer actually was not in Base64 format, but in DER binary format. Exporting it again in the right format worked. Nevertheless, it's pretty disturbing, that Postman accepts a file with the wrong format without complaining...

Emptyhanded

Answer 8

keep in mind ! this order might be an issue this will impact directly .

in program.cs file .....

app.UseAuthentication(); //first line should be

app.UseAuthorization(); //second line should be

correct order is above.

Guacin

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. – Calisa

Answer 9

In my case, I went to Settings > Certificates > enable CA certificates, then Select File and selected our bundle.crt file (not a PEM file) and it worked.

Contestant

Answer 10

Remove the whitespace at the end of the url.

This was the cause in my case and it took me hours to notice because I copy/paste the same url over and over again.

Why? I have no idea.

Pickwickian