Use creds as supplementary of individual parameters

[MoChilia]

Description

This pr is going to read creds from Json, the items in creds will not overwrite the individual parameters client-id, tenant-id and subscription-id, but as supplementary.

• In the previous code, creds is not compatible with individual parameters. We use creds for login using service principal with secret and individual parameters for OIDC login:
  

  login/src/main.ts

  Lines 78 to 93 in 990b22f

  	if (servicePrincipalId || tenantId || subscriptionId) {
  	//If few of the individual credentials (clent_id, tenat_id, subscription_id) are missing in action inputs.
  	if (!(servicePrincipalId && tenantId && (subscriptionId || allowNoSubscriptionsLogin)))
  	throw new Error("Few credentials are missing. ClientId, tenantId are mandatory. SubscriptionId is also mandatory if allow-no-subscriptions is not set.");
  	}
  	else {
  	if (creds) {
  	core.debug('using creds JSON...');
  	enableOIDC = false;
  	servicePrincipalId = secrets.getSecret("$.clientId", true);
  	servicePrincipalKey = secrets.getSecret("$.clientSecret", true);
  	tenantId = secrets.getSecret("$.tenantId", true);
  	subscriptionId = secrets.getSecret("$.subscriptionId", true);
  	resourceManagerEndpointUrl = secrets.getSecret("$.resourceManagerEndpointUrl", false);
  	}

  
  In the new version, we aim to fetch the user's input credentials as much as possible:
  

  login/src/common/LoginConfig.ts

  Lines 35 to 42 in b3bc91b

  	if (creds) {
  	core.debug('Reading creds in JSON...');
  	this.servicePrincipalId = this.servicePrincipalId ? this.servicePrincipalId : secrets.getSecret("$.clientId", false);
  	this.servicePrincipalKey = secrets.getSecret("$.clientSecret", false);
  	this.tenantId = this.tenantId ? this.tenantId : secrets.getSecret("$.tenantId", false);
  	this.subscriptionId = this.subscriptionId ? this.subscriptionId : secrets.getSecret("$.subscriptionId", false);
  	this.resourceManagerEndpointUrl = secrets.getSecret("$.resourceManagerEndpointUrl", false);
  	}

• We remove the boolean enableOIDC and use servicePrincipalKey to decide whether OIDC is enabled.

• We also remove the adjudication for undefined federatedToken in L122, since the error will be caught in L118. (Related to Support OIDC for sovereign clouds #321)
  

  login/src/main.ts

  Lines 115 to 129 in 990b22f

  	try{
  	federatedToken = await core.getIDToken(audience);
  	}
  	catch (error) {
  	core.error(`Please make sure to give write permissions to id-token in the workflow.`);
  	throw error;
  	}
  	if (!!federatedToken) {
  	let [issuer, subjectClaim] = await jwtParser(federatedToken);
  	console.log("Federated token details: \n issuer - " + issuer + " \n subject claim - " + subjectClaim);
  	}
  	else{
  	throw new Error("Failed to fetch federated token.");
  	}
  	}

[MoChilia]

Closed this pr, it is included in #336.