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Update A101: Fix the behavior for handling empty SNI value. #522

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Merged
kannanjgithub merged 2 commits into from
Mar 10, 2026
Merged

Update A101: Fix the behavior for handling empty SNI value. #522

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20a2e8c
Update A101-SNI-setting-and-SNI-SAN-validation.md
kannanjgithub Nov 24, 2025
9823806
Merge branch 'master' into kannanjgithub-patch-1
kannanjgithub Mar 10, 2026
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10 changes: 6 additions & 4 deletions A101-SNI-setting-and-SNI-SAN-validation.md
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Expand Up @@ -46,14 +46,16 @@ Tls connections using the fields from [UpstreamTlsContext][UTC] in the CDS updat

ii. Else, if `UpstreamTlsContext.sni` specifies the SNI to use, then it will be used.

iii. Else, no SNI will be set for the Tls handshake.
iii. Else, no SNI will be set for the Tls handshake. An empty string for SNI value will be treated as SNI not specified.

[UTC]: https://github.com/envoyproxy/envoy/blob/ee2bab9e40e7d7649cc88c5e1098c74e0c79501d/api/envoy/extensions/transport_sockets/tls/v3/tls.proto#L29
[A81-hostname]: A81-xds-authority-rewriting.md#xds-resource-validation

1. Server SAN validation against SNI used: If `auto_sni_san_validation` is true in the [UpstreamTlsContext][UTC]
gRPC client will perform matching for a SAN against the SNI used for the handshake. While `XdsChannelCredentials` without `auto_sni_san_validation` performs matching using any of DNS / URI / IPA SAN matchers specified in the validation context,
when `auto_sni_san_validation` is set, validation will be performed using exact DNS matcher.
Server SAN validation against SNI used: If `auto_sni_san_validation` is true in the [UpstreamTlsContext][UTC]
gRPC client will perform matching for a SAN against the SNI used for the handshake if any. If `auto_sni_san_validation` is true but no SNI was sent,
then validation will use any SAN matchers specified in the validation context instead.
While XdsChannelCredentials without auto_sni_san_validation performs matching using any of DNS / URI / IPA SAN matchers specified in the validation context,
when auto_sni_san_validation is set, validation will be performed using exact DNS matcher.

### Related Proposals:
* [gRFC A29: xDS-Based Security for gRPC Clients and Servers][A29]
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