Client Credential Authentication

Oct 13, 2025 by wbrum.org 107 views

OAuth Based Authentication Support for SMTP: A Solution to Microsoft's Retirement of Basic Authentication

Problem

The Retirement of Basic Authentication: A Challenge for Client Applications

Microsoft has announced its plan to permanently retire support for Basic authentication with Client Submission (SMTP AUTH) in Exchange Online by September 2025 [1][2]. This decision is a significant change for client applications that rely on Basic authentication for SMTP. As a result, these applications will be required to use OAuth for SMTP. Currently, the IS only supports Basic authentication for SMTP servers, and there is no option to configure OAuth-based authentication. This limitation poses a challenge for developers who need to integrate their applications with Microsoft 365 SMTP Server.

The Importance of OAuth-Based Authentication

OAuth-based authentication is a more secure and reliable method of authentication compared to Basic authentication. It provides a more robust way of authenticating users and authorizing access to resources. With OAuth, clients can obtain an access token that can be used to access protected resources without sharing their credentials. This approach reduces the risk of credential theft and phishing attacks. In the context of SMTP, OAuth-based authentication ensures that only authorized clients can send emails on behalf of a user.

Proposed Solution

Integrating OAuth-Based Authentication in the Email Provider Template

To address the retirement of Basic authentication, we propose integrating client credential and certificate-based authentication in addition to Basic authentication in the Email Provider template. This will enable developers to configure Microsoft 365 SMTP Server using OAuth-based authentication. The proposed solution involves the following steps:

Client Credential Authentication: This method involves using a client ID and client secret to obtain an access token. The client ID and client secret are registered with the Microsoft 365 tenant, and the access token is used to authenticate the client.
Certificate-Based Authentication: This method involves using a certificate to authenticate the client. The certificate is registered with the Microsoft 365 tenant, and the client uses the certificate to obtain an access token.
OAuth-Based Authentication Configuration: The Email Provider template will be modified to include an option to configure OAuth-based authentication. This will involve entering the client ID, client secret, or certificate details, depending on the chosen authentication method.

Benefits of the Proposed Solution

The proposed solution offers several benefits, including:

Improved Security: OAuth-based authentication provides a more secure way of authenticating clients and authorizing access to resources.
Reliability: OAuth-based authentication reduces the risk of credential theft and phishing attacks.
Flexibility: The proposed solution allows developers to choose between client credential and certificate-based authentication methods.
Compatibility: The proposed solution is compatible with Microsoft 365 SMTP Server and ensures seamless integration with the Email Provider template.

Alternatives

No response

Version

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Implementation Details

Technical Requirements

The proposed solution requires the following technical requirements:

Microsoft 365 Tenant: A Microsoft 365 tenant is required to register the client ID and client secret or certificate.
Email Provider Template: The Email Provider template will be modified to include an option to configure OAuth-based authentication.
Client Application: The client application will be modified to use OAuth-based authentication to send emails on behalf of a user.

Development Roadmap

The development roadmap for the proposed solution is as follows:

Research and Planning: Research the technical requirements and plan the development of the proposed solution.
Development: Develop the modified Email Provider template and client application to support OAuth-based authentication.
Testing: Test the proposed solution to ensure seamless integration with Microsoft 365 SMTP Server.
Deployment: Deploy the proposed solution to production.

Conclusion

The retirement of Basic authentication by Microsoft poses a challenge for client applications that rely on this method of authentication. To address this challenge, we propose integrating client credential and certificate-based authentication in addition to Basic authentication in the Email Provider template. This will enable developers to configure Microsoft 365 SMTP Server using OAuth-based authentication, providing a more secure and reliable method of authentication. The proposed solution offers several benefits, including improved security, reliability, flexibility, and compatibility with Microsoft 365 SMTP Server.
OAuth Based Authentication Support for SMTP: A Solution to Microsoft's Retirement of Basic Authentication

Q&A: OAuth Based Authentication Support for SMTP

Q: What is the retirement of Basic authentication by Microsoft?

A: Microsoft has announced its plan to permanently retire support for Basic authentication with Client Submission (SMTP AUTH) in Exchange Online by September 2025. This decision is a significant change for client applications that rely on Basic authentication for SMTP.

Q: Why is OAuth-based authentication more secure than Basic authentication?

A: OAuth-based authentication is more secure than Basic authentication because it provides a more robust way of authenticating users and authorizing access to resources. With OAuth, clients can obtain an access token that can be used to access protected resources without sharing their credentials. This approach reduces the risk of credential theft and phishing attacks.

Q: What are the benefits of using OAuth-based authentication for SMTP?

A: The benefits of using OAuth-based authentication for SMTP include:

Improved Security: OAuth-based authentication provides a more secure way of authenticating clients and authorizing access to resources.
Reliability: OAuth-based authentication reduces the risk of credential theft and phishing attacks.
Flexibility: The proposed solution allows developers to choose between client credential and certificate-based authentication methods.
Compatibility: The proposed solution is compatible with Microsoft 365 SMTP Server and ensures seamless integration with the Email Provider template.

Q: How does client credential authentication work?

A: Client credential authentication involves using a client ID and client secret to obtain an access token. The client ID and client secret are registered with the Microsoft 365 tenant, and the access token is used to authenticate the client.

Q: How does certificate-based authentication work?

A: Certificate-based authentication involves using a certificate to authenticate the client. The certificate is registered with the Microsoft 365 tenant, and the client uses the certificate to obtain an access token.

Q: What are the technical requirements for implementing OAuth-based authentication for SMTP?

A: The technical requirements for implementing OAuth-based authentication for SMTP include:

Microsoft 365 Tenant: A Microsoft 365 tenant is required to register the client ID and client secret or certificate.
Email Provider Template: The Email Provider template will be modified to include an option to configure OAuth-based authentication.
Client Application: The client application will be modified to use OAuth-based authentication to send emails on behalf of a user.

Q: What is the development roadmap for implementing OAuth-based authentication for SMTP?

A: The development roadmap for implementing OAuth-based authentication for SMTP is as follows:

Research and Planning: Research the technical requirements and plan the development of the proposed solution.
Development: Develop the modified Email Provider template and client application to support OAuth-based authentication.
Testing: Test the proposed solution to ensure seamless integration with Microsoft 365 SMTP Server.
Deployment: Deploy the proposed solution to production.

Q: What are the next steps for implementing OAuth-based authentication for SMTP?

A: The next steps for implementing OAuth-based authentication for SMTP include:

Registering the client ID and client secret or certificate with the Microsoft 365 tenant.
Modifying the Email Provider template to include an option to configure OAuth-based authentication.
Modifying the client application to use OAuth-based authentication to send emails on behalf of a user.
Testing the proposed solution to ensure seamless integration with Microsoft 365 SMTP Server.

Q: What are the benefits of implementing OAuth-based authentication for SMTP?

A: The benefits of implementing OAuth-based authentication for SMTP include:

Improved Security: OAuth-based authentication provides a more secure way of authenticating clients and authorizing access to resources.
Reliability: OAuth-based authentication reduces the risk of credential theft and phishing attacks.
Flexibility: The proposed solution allows developers to choose between client credential and certificate-based authentication methods.
Compatibility: The proposed solution is compatible with Microsoft 365 SMTP Server and ensures seamless integration with the Email Provider template.