Embedded Javascript (angular4) unable to get bearer token from Http Post - Error: CORs/[AADSTS90014]

Hello All;

I have been trying for a while to get an embedded solution to work, as a proof of concept. But I am struggling with the Http requests.

This is trying to follow the "App owns data" "example".

https://docs.microsoft.com/en-us/power-bi/developer/embed-sample-for-customers

I have created a Native application. I have given it the correct permissions, I used a global admin account, and I granted permissions within Azure Portal.

The following method works fine within PostMan (ie all the correct information is given). https://community.powerbi.com/t5/Developer/How-To-Get-embed-token-using-Get-Post-only/td-p/294475

However it fails when I try to call the first request (/oauth2/token) with Javascript. All parameters are identical, I have double and triple checked them. 

My code is as follows:

getAccessToken(Password): string{
    const url = "https://login.windows.net/{tenantID}/oauth2/token";
    const headers = new HttpHeaders( {
        "Content-Type": "application/x-www-form-urlencoded"
    });
    const requestBody = {
        "grant_type": "password",
        "scope": "openid",
        "resource": "https://analysis.windows.net/powerbi/api",
        "client_id": this.getClientID(),
        "username": this.getUsername(),
        "password": Password
    }
    var accessTokenRequestReponse = this.httpClient.post(url, requestBody, {headers: headers}).subscribe(
        (reponse) => {
            console.log(reponse)
            console.log(reponse['access_token'])
        },
        (error) => {console.log(error)}
    )
    return("");
}

https://login.windows.net/{tenantID}/oauth2/v2.0/token
https://login.windows.net/common/oauth2/v2.0/token
https://login.windows.net/{tenantID}/oauth2/token
https://login.windows.net/common/oauth2/token
https://login.microsoftonline.com/common/oauth2/token
https://login.microsoftonline.com/{tenantID}/oauth2/token

error:"invalid_request"
error_codes:[90014]
error_description:"AADSTS90014: The request body must contain the following parameter: 'grant_type'.
↵Trace ID: c4ce24c7-{...}d00
↵Correlation ID: 21a2c8d0-{...}87
↵Timestamp: 2018-04-26 {...}"

Accept: application/json, text/plain, */*
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Connection: keep-alive
Content-Length: 260
Content-Type: application/x-www-form-urlencoded
Host: login.windows.net
Origin: http://evil.com/ #Note this is from that chrome extenstion
Referer: http://localhost:4200/powerBI
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

{
  "grant_type":"password",
  "scope":"openid",
  "resource":"https://analysis.windows.net/powerbi/api",
  "client_id":"{clientID}",
  "username":"{username}@{tenant}.onmicrosoft.com",
  "password":"{password}",
  "tenant":"{tenant}.onmicrosoft.com"
}: