seikaikyo/implementing-zero-trust-for-saas-applications

Implementing Zero Trust for SaaS Applications

When to Use

• When securing access to SaaS applications (Microsoft 365, Google Workspace, Salesforce, Slack)
• When implementing conditional access policies requiring MFA and device compliance for SaaS
• When deploying CASB for shadow IT discovery and unsanctioned app blocking
• When enforcing session-level controls (DLP, download restrictions) for sensitive SaaS data
• When governing OAuth application permissions and detecting excessive consent grants

Do not use as a replacement for SaaS-native security controls (configure those first), for applications with no SAML/OIDC support, or when SaaS vendor does not support API integration for CASB/SSPM.

Prerequisites

• Identity provider with conditional access: Microsoft Entra ID P1/P2, Okta
• CASB solution: Microsoft Defender for Cloud Apps, Netskope, or Zscaler CASB
• SaaS applications configured with SSO via SAML 2.0 or OIDC
• MDM enrollment for device compliance signals (Intune, Jamf)
• DLP policies defined for sensitive data categories

Workflow

Step 1: Federate SaaS Authentication Through Identity Provider

Centralize authentication for all SaaS applications through a single IdP.

# Configure SAML SSO for Salesforce via Entra ID
Connect-MgGraph -Scopes "Application.ReadWrite.All"

# Create enterprise application for Salesforce
$app = New-MgServicePrincipal -AppId "SALESFORCE_APP_ID" -DisplayName "Salesforce"

# Configure SAML SSO settings
$samlSettings = @{
    preferredSingleSignOnMode = "saml"
    samlSingleSignOnSettings = @{
        relayState = ""
    }
}
Update-MgServicePrincipal -ServicePrincipalId $app.Id -BodyParameter $samlSettings

# Assign user groups to the application
New-MgServicePrincipalAppRoleAssignment -ServicePrincipalId $app.Id -BodyParameter @{
    principalId = "SALES_GROUP_ID"
    resourceId = $app.Id
    appRoleId = "DEFAULT_ROLE_ID"
}

Step 2: Create Conditional Access Policies for SaaS Applications

Enforce identity and device requirements before granting SaaS access.

# Block access from non-compliant devices to sensitive SaaS apps
$policy = @{
    displayName = "ZT - Require Compliant Device for SaaS"
    state = "enabled"
    conditions = @{
        applications = @{
            includeApplications = @("SALESFORCE_APP_ID", "M365_APP_ID", "SLACK_APP_ID")
        }
        users = @{
            includeUsers = @("All")
            excludeGroups = @("BREAK_GLASS_GROUP")
        }
        clientAppTypes = @("browser", "mobileAppsAndDesktopClients")
    }
    grantControls = @{
        operator = "AND"
        builtInControls = @("mfa", "compliantDevice")
    }
    sessionControls = @{
        cloudAppSecurity = @{
            isEnabled = $true
            cloudAppSecurityType = "mcasConfigured"
        }
        signInFrequency = @{
            value = 8
            type = "hours"
            isEnabled = $true
        }
    }
}
New-MgIdentityConditionalAccessPolicy -BodyParameter $policy

# Block downloads on unmanaged devices
$downloadPolicy = @{
    displayName = "ZT - Block Downloads on Unmanaged Devices"
    state = "enabled"
    conditions = @{
        applications = @{ includeApplications = @("SHAREPOINT_APP_ID") }
        users = @{ includeUsers = @("All") }
        devices = @{
            deviceFilter = @{
                mode = "include"
                rule = "device.isCompliant -ne True -or device.trustType -ne 'ServerAD'"
            }
        }
    }
    sessionControls = @{
        cloudAppSecurity = @{
            isEnabled = $true
            cloudAppSecurityType = "mcasConfigured"
        }
    }
}
New-MgIdentityConditionalAccessPolicy -BodyParameter $downloadPolicy

Step 3: Deploy CASB for Shadow IT Discovery and App Governance

Configure Microsoft Defender for Cloud Apps to discover and control SaaS usage.

# Query discovered cloud apps via Defender for Cloud Apps API
curl -X GET "https://api.cloudappsecurity.com/api/v1/discovery/" \
  -H "Authorization: Token ${MDCA_API_TOKEN}" \
  -H "Content-Type: application/json"

# Get list of unsanctioned apps
curl -X GET "https://api.cloudappsecurity.com/api/v1/discovery/discovered_apps/" \
  -H "Authorization: Token ${MDCA_API_TOKEN}" \
  -d '{
    "filters": {
      "appTag": {"eq": "unsanctioned"},
      "traffic": {"gte": 1000}
    },
    "sortField": "traffic",
    "sortDirection": "desc"
  }'

# Create session policy for DLP enforcement
curl -X POST "https://api.cloudappsecurity.com/api/v1/policies/" \
  -H "Authorization: Token ${MDCA_API_TOKEN}" \
  -d '{
    "name": "Block PII Upload to SaaS",
    "policyType": "SESSION",
    "severity": "HIGH",
    "enabled": true,
    "sessionPolicyType": "CONTROL_UPLOAD",
    "filters": {
      "fileType": {"eq": ["DOCUMENT", "SPREADSHEET"]},
      "contentInspection": {
        "dataType": ["CREDIT_CARD", "SSN", "PASSPORT"]
      }
    },
    "actions": {
      "block": true,
      "notify": {
        "emailRecipients": ["[email protected]"]
      }
    }
  }'

Step 4: Configure OAuth App Governance

Review and restrict OAuth application permissions to prevent excessive consent.

# Query OAuth apps with high-privilege permissions
$oauthApps = Invoke-MgGraphRequest -Method GET `
  "https://graph.microsoft.com/v1.0/servicePrincipals?\$filter=tags/any(t:t eq 'WindowsAzureActiveDirectoryIntegratedApp')&\$select=displayName,appId,oauth2PermissionScopes"

# Review consent grants
$grants = Get-MgOauth2PermissionGrant -All
$highRisk = $grants | Where-Object {
    $_.Scope -match "Mail.ReadWrite|Files.ReadWrite.All|Directory.ReadWrite.All"
}

Write-Host "High-risk OAuth grants: $($highRisk.Count)"
$highRisk | ForEach-Object {
    $sp = Get-MgServicePrincipal -ServicePrincipalId $_.ClientId
    Write-Host "  App: $($sp.DisplayName) | Scope: $($_.Scope) | Type: $($_.ConsentType)"
}

# Configure app consent policy to require admin approval
$consentPolicy = @{
    displayName = "Require Admin Approval for High-Risk Permissions"
    conditions = @{
        clientApplications = @{ includeAllClientApplications = $true }
        permissions = @{
            permissionClassification = "high"
            permissions = @(
                @{ permissionValue = "Mail.ReadWrite"; permissionType = "delegated" }
                @{ permissionValue = "Files.ReadWrite.All"; permissionType = "delegated" }
            )
        }
    }
}

Step 5: Implement SaaS Security Posture Management (SSPM)

Audit and remediate SaaS security configuration drift.

# Query SaaS security posture via CASB API
curl -X GET "https://api.cloudappsecurity.com/api/v1/security_config/" \
  -H "Authorization: Token ${MDCA_API_TOKEN}" \
  -d '{"app": "Microsoft 365"}'

# Common SSPM checks:
# - MFA enforcement for all admin accounts
# - External sharing restrictions in SharePoint/OneDrive
# - Email forwarding rules to external domains blocked
# - Idle session timeout configured (< 8 hours)
# - Legacy authentication protocols disabled
# - Admin consent workflow enabled
# - Conditional access policies active
# - Audit logging enabled for all services

Key Concepts

| Term | Definition | |------|------------| | CASB | Cloud Access Security Broker - intermediary enforcing security policies between users and SaaS applications | | SSPM | SaaS Security Posture Management - continuous monitoring of SaaS application security configurations | | OAuth Governance | Review and control of third-party application permissions granted through OAuth consent flows | | Session Controls | Real-time access restrictions (block downloads, DLP inspection, watermarking) applied during active SaaS sessions | | Shadow IT | Unauthorized SaaS applications used by employees without IT approval or security review | | Conditional Access | Policy engine evaluating identity, device, location, and risk signals before granting SaaS access |

Tools & Systems

• Microsoft Defender for Cloud Apps: CASB providing shadow IT discovery, session controls, DLP, and SSPM
• Microsoft Entra ID Conditional Access: Policy engine for identity-based access control to SaaS applications
• Netskope CASB: Cloud-native CASB with inline and API-based SaaS security controls
• Okta Identity Governance: OAuth app governance and access certification for SaaS applications
• SSPM Tools: AppOmni, Adaptive Shield, Valence Security for SaaS configuration monitoring

Common Scenarios

Scenario: Securing Microsoft 365 and Salesforce for 1,000-User Organization

Context: A professional services firm with 1,000 users uses Microsoft 365, Salesforce, Slack, and 20+ other SaaS apps. Several data breaches in the industry drive a zero trust initiative for all SaaS access.

Approach:

1. Federate all SaaS authentication through Entra ID with SAML SSO
2. Create conditional access policies requiring MFA + compliant device for all SaaS apps
3. Deploy Defender for Cloud Apps for shadow IT discovery (identify 150+ unauthorized apps)
4. Mark unauthorized apps as unsanctioned and block via SWG/proxy
5. Configure session controls: block downloads on unmanaged devices, DLP for file uploads
6. Review OAuth app permissions: revoke 45 high-risk consent grants, enable admin approval workflow
7. Enable SSPM monitoring for Microsoft 365 and Salesforce configurations
8. Set up weekly automated posture reports for security leadership

Pitfalls: Conditional access policies need break-glass exclusions. Some legacy SaaS apps may not support modern authentication. Session controls require proxy-based CASB which can impact performance. OAuth app revocation may break integrations; coordinate with app owners first.

Output Format

Zero Trust SaaS Security Report
==================================================
Organization: ProServices Corp
Report Date: 2026-02-23

SAAS INVENTORY:
  Sanctioned Apps: 25
  Unsanctioned (blocked): 127
  Shadow IT Users: 342 (discovered in last 30 days)

CONDITIONAL ACCESS:
  Policies active: 8
  Sign-ins evaluated: 456,789
  Blocked by policy: 2,345 (0.5%)
  MFA enforced: 100% of sign-ins

DEVICE COMPLIANCE:
  Compliant device required: All 25 sanctioned apps
  Sign-ins from compliant: 448,123 (98.1%)
  Sign-ins blocked (non-compliant): 8,666

CASB / DLP:
  DLP violations detected: 89
  Files blocked from upload: 34
  Downloads blocked (unmanaged): 1,234

OAUTH GOVERNANCE:
  Total OAuth apps: 312
  High-risk permissions: 12 (reviewed)
  Revoked consents: 45
  Pending admin approval: 8

SSPM FINDINGS:
  Critical misconfigurations: 3
  High: 7
  Medium: 15
  Remediated this month: 18