Angular with Azure AD B2C Audience Validation Failed - asp.net-core

Question

I have an Anuglar5 spa frontend and ASP.NET Core API. Both secured by Azure AD B2C service. The angular application redirects correctly to the login page and signing in returns a token. When I try to call the API with the token I get;
AuthenticationFailed: IDX10214: Audience validation failed. Audiences: '627684f5-5011-475a-9cbd-55fcdcdf369e'. Did not match: validationParameters.ValidAudience: 'ee8b98a0-ae7a-38b2-9e73-d175df22ef4c' or validationParameters.ValidAudiences: 'null'.
"627684f5-5011-475a-9cbd-55fcdcdf369e" is the Application ID of the frontend app. And "ee8b98a0-ae7a-38b2-9e73-d175df22ef4c" is the Application ID of the API.
My code;
`export class MSALService {
private applicationConfig: any = {
clientID: '627684f5-5011-475a-9cbd-55fcdcdf369e',
authority: 'https://login.microsoftonline.com/tfp/mytenant.onmicrosoft.com/B2C_1_my_signin_signup',
b2cScopes: ['https://meeblitenant.onmicrosoft.com/api/myapp_read', 'https://meeblitenant.onmicrosoft.com/api/myapp_write'],
redirectUrl: 'http://localhost:4200/'
};
private app: any;
public user: any;
constructor() {
this.app = new UserAgentApplication(this.applicationConfig.clientID, this.applicationConfig.authority,
(errorDesc, token, error, tokenType) => {
console.log(token);
},
{ redirectUri: this.applicationConfig.redirectUrl }
);
}
public login() {
let tokenData = '';
this.app.loginRedirect(this.applicationConfig.b2cScopes).then(data => { tokenData = data; });
}
public getUser() {
const user = this.app.getUser();
if (user) {
return user;
} else {
return null;
}
}
public logout() {
this.app.logout();
}
public getToken() {
return this.app.acquireTokenSilent(this.applicationConfig.b2cScopes)
.then(accessToken => {
console.log(accessToken);
return accessToken;
}, error => {
return this.app.acquireTokenPopup(this.applicationConfig.b2cScopes)
.then(accessToken => {
return accessToken;
}, err => {
console.error(err);
});
}
);
}
}`
Using the token that is returned in Postman also returns the same error. My theory is that the URL I am using to call Azure AD B2C is the problem but looking through the docs I cannot find the problem.
Any help would be greatly appreciated.

Answer 1

Kinda sounds like you are sending the Id token to the API (which is meant for your front-end) instead of an access token. You can debug the issue further by decoding the token you get at https://jwt.ms.
There the aud (audience) should match your API's id, and the scopes you asked should also be there.