I am implementing the authorization code flow with Nestjs and keycloak, I have already redirected the login request to the keycloak login page, I received the authorization code and when making the post to the callback url, I get the following error:

Converting circular structure to JSON
-> starting at object with constructor 'ClientRequest'
| property 'socket' -> object with constructor 'Socket'
--- property '_httpMessage' closes the circle

I noticed that this error happens only after passing the authorization code as a parameter:

follow the code:

import { HttpException, HttpService, Injectable } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { KeycloakConnectModule } from 'nest-keycloak-connect';
import * as queryString from 'querystring'
import { catchError } from 'rxjs/operators';

@Injectable()
export class AuthService {

private keycloakLoginUri: string;
private keycloakResponseType: string;
private keycloakScope: string;
private keycloakRedirectUri: string;
private keycloakGrantType: string;
private keycloakClientId: string;
private keycloakClientSecret: string;
private keycloakTokenUri: string;

constructor(  readonly _config: ConfigService, private readonly _http: HttpService) {
    this.keycloakLoginUri = _config.get('KEYCLOAK_LOGIN_URI');
    this.keycloakResponseType = _config.get('KEYCLOAK_RESPONSE_TYPE');
    this.keycloakScope = _config.get('KEYCLOAK_SCOPE');
    this.keycloakRedirectUri = _config.get('KEYCLOAK_REDIRECT_URI');
    this.keycloakGrantType = 'authorization_code';
    this.keycloakClientId = _config.get('KEYCLOAK_CLIENT_ID'); 
    this.keycloakClientSecret = _config.get('KEYCLOAK_CLIENT_SECRET');
    this.keycloakTokenUri = this._config.get('KEYCLOAK_TOKEN_URI');
}

getLoginUrl(): any {
    return { url: `${this.keycloakLoginUri}`
        +`?client_id=${this.keycloakClientId}`
        +`&response_type=${this.keycloakResponseType}`
        +`&scope=${this.keycloakScope}`
        +`&redirect_uri=${this.keycloakRedirectUri}`
    }
}

getKeyCloakToken(code: string){
    const params =  {
        grant_type: this.keycloakGrantType,
        client_id: this.keycloakClientId,
        client_secret: this.keycloakClientSecret,
        code: code,
        redirect_uri: this.keycloakRedirectUri
    };

    const config = {
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded'
        }
    }

    
    return this._http.post(
        this.keycloakTokenUri, 
        queryString.stringify(params),
        config)
    .pipe(catchError(e => {
        throw new HttpException(e.response.data, e.response.status);
    }));
}
}

Enviroments variables defined on .env:

KEYCLOAK_LOGIN_URI=http://localhost:8080/auth/realms/onboarding-arqt/protocol/openid-connect/auth
KEYCLOAK_AUTH_URI=http://localhost:8080/auth
KEYCLOAK_TOKEN_URI=http://localhost:8080/auth/realms/onboarding-arqt/protocol/openid-connect/token?
KEYCLOAK_GRANT_TYPE=authorization_code
KEYCLOAK_REALM=my-realm
KEYCLOAK_CLIENT_ID=my-id
KEYCLOAK_CLIENT_SECRET=my-secret
KEYCLOAK_REDIRECT_URI=http://localhost:3000/callback
KEYCLOAK_SCOPE=profile
KEYCLOAK_RESPONSE_TYPE=code